A stack buffer overflow may lead to a crash, causing Denial of Service, or potentially remote code execution.

When parsing CMS AuthEnvelopedData structures that use AEAD ciphers such as AES-GCM, the IV (Initialization Vector) encoded in the ASN.1 parameters is copied into a fixed-size stack buffer without verifying that its length fits the destination. An attacker can supply a crafted CMS message with an oversized IV, causing a stack-based out-of-bounds write before any authentication or tag verification occurs.

Applications and services that parse untrusted CMS or PKCS#7 content using AEAD ciphers (e.g., S/MIME AuthEnvelopedData with AES-GCM) are vulnerable. Because the overflow occurs prior to authentication, no valid key material is required to trigger it. While exploitability to remote code execution depends on platform and toolchain mitigations, the stack-based write primitive represents a severe risk.

The FIPS modules in 3.6, 3.5, 3.4, 3.3 and 3.0 are not affected by this issue, as the CMS implementation is outside the OpenSSL FIPS module boundary.

OpenSSL 3.6, 3.5, 3.4, 3.3 and 3.0 are vulnerable to this issue.

OpenSSL 1.1.1 and 1.0.2 are not affected by this issue.

OpenSSL 3.6 users should upgrade to OpenSSL 3.6.1.

OpenSSL 3.5 users should upgrade to OpenSSL 3.5.5.

OpenSSL 3.4 users should upgrade to OpenSSL 3.4.4.

OpenSSL 3.3 users should upgrade to OpenSSL 3.3.6.

OpenSSL 3.0 users should upgrade to OpenSSL 3.0.19.

Heap Buffer Overflow in Hexadecimal Conversion

Issue summary: OpenSSL CMP response validation passed an unexpected response sender distinguished name directly as the format string to ERRraisedata().

Issue summary: Applications using AES-CFB128 encryption or decryption on systems with AVX-512 and VAES support can trigger an out-of-bounds read of up to 15 bytes when processing partial cipher blocks.

Impact summary: This out-of-bounds read may trigger a crash which leads to Denial of Service for an application if the input buffer ends at a memory page boundary and the following page is unmapped. There is no information disclosure as the over-read bytes are not written to output.

The vulnerable code path is only reached when processing partial blocks (when a previous call left an incomplete block and the current call provides fewer bytes than needed to complete it). Additionally, the input buffer must be positioned at a page boundary with the following page unmapped. CFB mode is not used in TLS/DTLS protocols, which use CBC, GCM, CCM, or ChaCha20-Poly1305 instead. For these reasons the issue was assessed as Low severity according to our Security Policy.

Only x86-64 systems with AVX-512 and VAES instruction support are affected. Other architectures and systems without VAES support use different code paths that are not affected.

OpenSSL FIPS module in 3.6 version is affected by this issue.

CMS AuthEnvelopedData Processing May Accept Forged Messages

Issue summary: ChaCha20-Poly1305 and AES-OCB decryption with an empty ciphertext can report success without verifying the supplied authentication tag when the operation is finalized by calling the EVPCipher() function.

Heap Use-After-Free in OpenSSL PKCS7verify()

Heap Use-After-Free in OpenSSL PKCS7verify() (CVE-2026-45447) Severity: High

Issue summary: A specially crafted PKCS#7 or S/MIME signed message could trigger a use-after-free during PKCS#7 signature verification.

Impact summary: A use-after-free may result in process crashes, heap corruption, or potentially remote code execution.

When processing a PKCS#7 or S/MIME signed message, if the SignedData digestAlgorithms field is present as an empty ASN.1 SET, OpenSSL may incorrectly free a caller-owned BIO during PKCS7verify(). A subsequent use of the BIO by the calling application results in a use-after-free condition.

In the common case this occurs when the application later calls BIOfree() on the BIO originally passed to PKCS7verify(). Depending on allocator behavior and application-specific BIO usage patterns, this may result in a crash or other memory corruption. In some application contexts this may potentially be exploitable for remote code execution.

Applications that process PKCS#7 or S/MIME signed messages using OpenSSL PKCS#7 APIs may be affected. Applications using the CMS APIs for this processing are not affected.

The FIPS modules in 4.0, 3.6, 3.5, 3.4, and 3.0 are not affected by this issue, as the affected code is outside the OpenSSL FIPS module boundary.

OpenSSL 4.0, 3.6, 3.5, 3.4, 3.0, 1.1.1, and 1.0.2 are vulnerable to this issue.

OpenSSL 4.0 users should upgrade to OpenSSL 4.0.1 OpenSSL 3.6 users should upgrade to OpenSSL 3.6.3. OpenSSL 3.5 users should upgrade to OpenSSL 3.5.7. OpenSSL 3.4 users should upgrade to OpenSSL 3.4.6. OpenSSL 3.0 users should upgrade to OpenSSL 3.0.21. OpenSSL 1.1.1 users should upgrade to OpenSSL 1.1.1zh (premium support customers only). OpenSSL 1.0.2 users should upgrade to OpenSSL 1.0.2zq (premium support customers only).

This issue was reported by Thai Duong (Calif.io in collaboration with Claude and Anthropic Research). on 27th April 2026. The fix was developed by Igor Ustinov.

Issue summary: An uncommon configuration of clients performing DANE TLSA-based server authentication, when paired with uncommon server DANE TLSA records, may result in a use-after-free and/or double-free on the client side.

Impact summary: A use after free can have a range of potential consequences such as the corruption of valid data, crashes or execution of arbitrary code.

However, the issue only affects clients that make use of TLSA records with both the PKIX-TA(0/PKIX-EE(1) certificate usages and the DANE-TA(2) certificate usage.

By far the most common deployment of DANE is in SMTP MTAs for which RFC7672 recommends that clients treat as 'unusable' any TLSA records that have the PKIX certificate usages. These SMTP (or other similar) clients are not vulnerable to this issue. Conversely, any clients that support only the PKIX usages, and ignore the DANE-TA(2) usage are also not vulnerable.

The client would also need to be communicating with a server that publishes a TLSA RRset with both types of TLSA records.

No FIPS modules are affected by this issue, the problem code is outside the FIPS module boundary.

Issue summary: A signed integer overflow when sizing the destination buffer for Unicode output in ASN1mbstringncopy() can lead to a heap buffer overflow.

Issue summary: A type confusion vulnerability exists in the TimeStamp Response verification code where an ASN1TYPE union member is accessed without first validating the type, causing an invalid or NULL pointer dereference when processing a malformed TimeStamp Response file.

Impact summary: An application calling TSRESPverifyresponse() with a malformed TimeStamp Response can be caused to dereference an invalid or NULL pointer when reading, resulting in a Denial of Service.

The functions osslessgetsigningcert() and osslessgetsigningcertv2() access the signing cert attribute value without validating its type. When the type is not VASN1SEQUENCE, this results in accessing invalid memory through the ASN1TYPE union, causing a crash.

Exploiting this vulnerability requires an attacker to provide a malformed TimeStamp Response to an application that verifies timestamp responses. The TimeStamp protocol (RFC 3161) is not widely used and the impact of the exploit is just a Denial of Service. For these reasons the issue was assessed as Low severity.

The FIPS modules in 3.5, 3.4, 3.3 and 3.0 are not affected by this issue, as the TimeStamp Response implementation is outside the OpenSSL FIPS module boundary.

OpenSSL 3.6, 3.5, 3.4, 3.3, 3.0 and 1.1.1 are vulnerable to this issue.

OpenSSL 1.0.2 is not affected by this issue.

Issue summary: Processing a malformed PKCS#12 file can trigger a NULL pointer dereference in the PKCS12itemdecryptd2iex() function.

Impact summary: A NULL pointer dereference can trigger a crash which leads to Denial of Service for an application processing PKCS#12 files.

The PKCS12itemdecryptd2iex() function does not check whether the oct parameter is NULL before dereferencing it. When called from PKCS12unpackp7encdata() with a malformed PKCS#12 file, this parameter can be NULL, causing a crash. The vulnerability is limited to Denial of Service and cannot be escalated to achieve code execution or memory disclosure.

Exploiting this issue requires an attacker to provide a malformed PKCS#12 file to an application that processes it. For that reason the issue was assessed as Low severity according to our Security Policy.

The FIPS modules in 3.6, 3.5, 3.4, 3.3 and 3.0 are not affected by this issue, as the PKCS#12 implementation is outside the OpenSSL FIPS module boundary.

OpenSSL 3.6, 3.5, 3.4, 3.3, 3.0, 1.1.1 and 1.0.2 are vulnerable to this issue.

Issue summary: During processing of a crafted CMS EnvelopedData message with KeyAgreeRecipientInfo a NULL pointer dereference can happen.

Impact summary: Applications that process attacker-controlled CMS data may crash before authentication or cryptographic operations occur resulting in Denial of Service.

When a CMS EnvelopedData message that uses KeyAgreeRecipientInfo is processed, the optional parameters field of KeyEncryptionAlgorithmIdentifier is examined without checking for its presence. This results in a NULL pointer dereference if the field is missing.

Applications and services that call CMSdecrypt() on untrusted input (e.g., S/MIME processing or CMS-based protocols) are vulnerable.

The FIPS modules in 3.6, 3.5, 3.4, 3.3 and 3.0 are not affected by this issue, as the affected code is outside the OpenSSL FIPS module boundary.

Incorrect Failure Handling in RSA KEM RSASVE Encapsulation

Issue summary: When a delta CRL that contains a Delta CRL Indicator extension is processed a NULL pointer dereference might happen if the required CRL Number extension is missing.

Impact summary: A NULL pointer dereference can trigger a crash which leads to a Denial of Service for an application.

When CRL processing and delta CRL processing is enabled during X.509 certificate verification, the delta CRL processing does not check whether the CRL Number extension is NULL before dereferencing it. When a malformed delta CRL file is being processed, this parameter can be NULL, causing a NULL pointer dereference.

Exploiting this issue requires the X509VFLAGUSEDELTAS flag to be enabled in the verification context, the certificate being verified to contain a freshestCRL extension or the base CRL to have the EXFLAGFRESHEST flag set, and an attacker to provide a malformed CRL to an application that processes it.

The vulnerability is limited to Denial of Service and cannot be escalated to achieve code execution or memory disclosure. For that reason the issue was assessed as Low severity according to our Security Policy.

The FIPS modules in 3.6, 3.5, 3.4, 3.3 and 3.0 are not affected by this issue, as the affected code is outside the OpenSSL FIPS module boundary.

Issue summary: During processing of a crafted CMS EnvelopedData message with KeyTransportRecipientInfo a NULL pointer dereference can happen.

Impact summary: Applications that process attacker-controlled CMS data may crash before authentication or cryptographic operations occur resulting in Denial of Service.

When a CMS EnvelopedData message that uses KeyTransportRecipientInfo with RSA-OAEP encryption is processed, the optional parameters field of RSA-OAEP SourceFunc algorithm identifier is examined without checking for its presence. This results in a NULL pointer dereference if the field is missing.

Applications and services that call CMSdecrypt() on untrusted input (e.g., S/MIME processing or CMS-based protocols) are vulnerable.

The FIPS modules in 3.6, 3.5, 3.4, 3.3 and 3.0 are not affected by this issue, as the affected code is outside the OpenSSL FIPS module boundary.

Issue summary: Receiving a QUIC initial packet with an invalid token may trigger a NULL pointer dereference in the OpenSSL QUIC server with address validation disabled.

Impact summary: NULL pointer dereference typically causes abnormal termination of the affected QUIC server process and a Denial of Service.

If the address validation is disabled in the OpenSSL QUIC server implementation, an attacker can crash the server by sending an initial packet with an invalid or expired token.

By default, the client address validation is enabled in the OpenSSL QUIC server implementation, which makes the default configuration not vulnerable to this issue. However if the SSLLISTENERFLAGNOVALIDATE is used with the SSLnewlistener() call, the address validation is disabled making the vulnerable code reachable.

The FIPS modules in 4.0, 3.6, 3.5, 3.4, and 3.0 are not affected by this issue, as the affected code is outside the OpenSSL FIPS module boundary.

Issue summary: When a partial-chain certificate verification is enabled together with OCSP response checking for the whole chain, a NULL dereference will happen if the verified chain does not have a self-signed trusted anchor, crashing the process.

Impact summary: A NULL pointer dereference can trigger a crash which leads to a Denial of Service for an application.

When performing OCSP response checking for certificates in the verification chain, the code always tries to access the next certificate as the issuer. There is a check for a self-signed certificate. However with the partial chain verification enabled when the chain does not have a self-signed trusted anchor, the issuer will be NULL for the last certificate in the chain. A NULL pointer dereference then happens.

This issue affects only applications which enable both OCSP verification of the certificate chain (X509VFLAGOCSPRESPCHECKALL) and partial chain verification (X509VFLAGPARTIALCHAIN) in the certificate verification. Both flags are disabled by default. For that reason, we have assigned Low severity to the issue.

No FIPS modules are affected by this issue as the affected code is outside the OpenSSL FIPS module boundary.

Issue summary: Remote peer may exhaust heap memory of the QUIC server or client by flooding it with packets containing PATHCHALLENGE frames.

Impact summary: A malicious remote peer can cause an unbounded memory allocation which can lead to an abnormal termination of the application acting as a QUIC client or server and a Denial of Service.

A remote peer may exhaust heap memory by flooding the local QUIC stack with PATHCHALLENGE frames. The local QUIC stack allocates a PATHRESPONSE frame for every PATHCHALLENGE it receives. The allocated PATHRESPONSE frame gets freed only when the remote peer acknowledges reception of the PATHRESPONSE frame which will not be done by a malicious peer.

The FIPS modules in 4.0, 3.6, 3.5, 3.4, and 3.0 are not affected by this issue. The QUIC stack is outside of OpenSSL FIPS module boundary.

Heap Buffer Over-read in ASN.1 Content Parsing

AES-OCB IV Ignored on EVPCipher() Path

Issue summary: When CMS password-based decryption (RFC 3211 / PWRI key unwrap) processes attacker-supplied CMS data, an attacker-chosen stream-mode KEK cipher can trigger a heap out-of-bounds read in kekunwrapkey().

Issue summary: In a server or client configuration with RFC7250 Raw Public Keys (RPKs) enabled, and only the private key (with no associated certificate) configured locally, a NULL pointer dereference may occur when the remote peer solicits raw public keys and also sends the typically omitted "signaturealgorithmscert" TLS extension.

Heap Buffer Overflow in CMS Key Unwrapping

Issue summary: QUIC server may double free QRX (QUIC record layer RX) object when channel creation fails for initial packet.

Invalid Pointer Dereference in CMP Server via Crafted protectionAlg

Issue summary: When OpenSSL processes QUIC traffic from a peer that repeatedly sends ack-eliciting packets while not acknowledging ACK-only responses, the QUIC stack can retain ACK-only packet metadata for the lifetime of the connection.

Excessive Memory Use Buffering DTLS Records for a Future Epoch

Issue summary: Calling PKCS12getfriendlyname() function on a maliciously crafted PKCS#12 file with a BMPString (UTF-16BE) friendly name containing non-ASCII BMP code point can trigger a one byte write before the allocated buffer.

Impact summary: The out-of-bounds write can cause a memory corruption which can have various consequences including a Denial of Service.

The OPENSSLuni2utf8() function performs a two-pass conversion of a PKCS#12 BMPString (UTF-16BE) to UTF-8. In the second pass, when emitting UTF-8 bytes, the helper function bmptoutf8() incorrectly forwards the remaining UTF-16 source byte count as the destination buffer capacity to UTF8putc(). For BMP code points above U+07FF, UTF-8 requires three bytes, but the forwarded capacity can be just two bytes. UTF8putc() then returns -1, and this negative value is added to the output length without validation, causing the length to become negative. The subsequent trailing NUL byte is then written at a negative offset, causing write outside of heap allocated buffer.

The vulnerability is reachable via the public PKCS12getfriendlyname() API when parsing attacker-controlled PKCS#12 files. While PKCS12parse() uses a different code path that avoids this issue, PKCS12getfriendlyname() directly invokes the vulnerable function. Exploitation requires an attacker to provide a malicious PKCS#12 file to be parsed by the application and the attacker can just trigger a one zero byte write before the allocated buffer. For that reason the issue was assessed as Low severity according to our Security Policy.

The FIPS modules in 3.6, 3.5, 3.4, 3.3 and 3.0 are not affected by this issue, as the PKCS#12 implementation is outside the OpenSSL FIPS module boundary.

OpenSSL 3.6, 3.5, 3.4, 3.3, 3.0 and 1.1.1 are vulnerable to this issue.

OpenSSL 1.0.2 is not affected by this issue.

Issue Summary: The PKCS#12 file processing fails to perform sufficient input validation for files that use Password-Based Message Authentication Code 1 (PBMAC1) integrity mechanism allowing a certificate and private key forgery.

Impact Summary: An attacker impersonating a user can cause a service reading PKCS#12 files to accept forged certificates and private keys with a 1 in 256 probability.

If a service accepting PKCS#12 files is using passwords for authenticating the received files, the attacker can create unencrypted PKCS#12 files that use PBMAC1 authentication that specifies an HMAC key of only one byte, allowing them to craft a file that will be accepted with a 1 in 256 probability. That would then cause the service to accept a certificate and private key controlled by the attacker.

The FIPS modules are not affected by this issue, as the affected code is outside the OpenSSL FIPS module boundary.

Issue summary: An OpenSSL TLS 1.3 server may fail to negotiate the expected preferred key exchange group when its key exchange group configuration includes the default by using the 'DEFAULT' keyword.

Impact summary: A less preferred key exchange may be used even when a more preferred group is supported by both client and server, if the group was not included among the client's initial predicated keyshares. This will sometimes be the case with the new hybrid post-quantum groups, if the client chooses to defer their use until specifically requested by the server.

If an OpenSSL TLS 1.3 server's configuration uses the 'DEFAULT' keyword to interpolate the built-in default group list into its own configuration, perhaps adding or removing specific elements, then an implementation defect causes the 'DEFAULT' list to lose its 'tuple' structure, and all server-supported groups were treated as a single sufficiently secure 'tuple', with the server not sending a Hello Retry Request (HRR) even when a group in a more preferred tuple was mutually supported.

As a result, the client and server might fail to negotiate a mutually supported post-quantum key agreement group, such as 'X25519MLKEM768', if the client's configuration results in only 'classical' groups (such as 'X25519' being the only ones in the client's initial keyshare prediction).

OpenSSL 3.5 and later support a new syntax for selecting the most preferred TLS 1.3 key agreement group on TLS servers. The old syntax had a single 'flat' list of groups, and treated all the supported groups as sufficiently secure. If any of the keyshares predicted by the client were supported by the server the most preferred among these was selected, even if other groups supported by the client, but not included in the list of predicted keyshares would have been more preferred, if included.

The new syntax partitions the groups into distinct 'tuples' of roughly equivalent security. Within each tuple the most preferred group included among the client's predicted keyshares is chosen, but if the client supports a group from a more preferred tuple, but did not predict any corresponding keyshares, the server will ask the client to retry the ClientHello (by issuing a Hello Retry Request or HRR) with the most preferred mutually supported group.

The above works as expected when the server's configuration uses the built-in default group list, or explicitly defines its own list by directly defining the various desired groups and group 'tuples'.

No OpenSSL FIPS modules are affected by this issue, the code in question lies outside the FIPS boundary.

OpenSSL 3.6 and 3.5 are vulnerable to this issue.

OpenSSL 3.6 users should upgrade to OpenSSL 3.6.2 once it is released. OpenSSL 3.5 users should upgrade to OpenSSL 3.5.6 once it is released.

OpenSSL 3.4, 3.3, 3.0, 1.0.2 and 1.1.1 are not affected by this issue.