ECDSA remote timing attack

A vulnerability was found in OpenSSL 1.0.2. When an application encounters a fatal protocol error and then calls SSLshutdown() twice, OpenSSL can respond differently to the calling application if a 0 byte record is received with invalid padding compared to if a 0 byte record is received with an invalid MAC. This difference in behaviour can be detected by a remote peer, then this amounts to a padding oracle that could be used to decrypt data. In order for this to be exploitable "non-stitched" ciphersuites must be in use. Also the application must call SSLshutdown() twice even if a protocol error has occurred (applications should not do this but some do anyway). AEAD ciphersuites are not impacted. This issue does not impact OpenSSL 1.1.1 or 1.1.0.

Upstream bug: https://www.openssl.org/news/secadv/20190226.txt

Upstream Patch: https://github.com/openssl/openssl/commit/e9bbefbf0f24c57645e7ad6a5a71ae649d18ac8e

An integer overflow was found in the x6464 Montgomery squaring procedure used in exponentiation with 512-bit moduli. As per upstream: No EC algorithms are affected. Attacks against 2-prime RSA1024, 3-prime RSA1536, and DSA1024 as a result of this defect would be very difficult to perform and are not believed likely. Attacks against DH512 are considered just feasible. However, for an attack the target would have to re-use the DH512 private key, which is not recommended anyway. Also applications directly using the low level API BNmodexp may be affected if they use BNFLGCONSTTIME

A flaw was found in OpenSSL versions from 1.1.0 through 1.1.0i inclusive, from 1.0.2 through 1.0.2p inclusive and version 1.1.1. The OpenSSL DSA signature algorithm has been shown to be vulnerable to a timing side channel attack. An attacker could use variations in the signing algorithm to recover the private key.

Reference: https://www.openssl.org/news/secadv/20181030.txt

Upstream Patches: https://git.openssl.org/gitweb/?p=openssl.git;a=commitdiff;h=43e6a58d4991a451daf4891ff05a48735df871ac https://git.openssl.org/gitweb/?p=openssl.git;a=commitdiff;h=8abfe72e8c1de1b95f50aa0d9134803b4d00070f https://git.openssl.org/gitweb/?p=openssl.git;a=commitdiff;h=ef11e19d1365eea2b1851e6f540a0bf365d303e7 https://github.com/openssl/openssl/commit/b96bebacfe814deb99fb64a3ed2296d95c573600

Last updated 25 August 2025

Constructed ASN.1 types with a recursive definition (such as can be found in PKCS7) could eventually exceed the stack given malicious input with excessive recursion. This could result in a Denial Of Service attack. There are no such structures used within SSL/TLS that come from untrusted sources so this is considered safe. Fixed in OpenSSL 1.1.0h (Affected 1.1.0-1.1.0g). Fixed in OpenSSL 1.0.2o (Affected 1.0.2b-1.0.2n).

OpenSSL could allow a remote attacker to obtain sensitive information, caused by an overflow bug in the AVX2 Montgomery multiplication procedure used in exponentiation with 1024-bit moduli. An attacker could exploit this vulnerability to obtain information about the private key.

Note: In order to exploit this vulnerability, the server would have to share the DH1024 private key among multiple clients, which is no longer an option since CVE-2016-0701.

Last updated 24 July 2024

OpenSSL 1.0.2 (starting from version 1.0.2b) introduced an "error state" mechanism. The intent was that if a fatal error occurred during a handshake then OpenSSL would move into the error state and would immediately fail if you attempted to continue the handshake. This works as designed for the explicit handshake functions (SSLdohandshake(), SSLaccept() and SSLconnect()), however due to a bug it does not work correctly if SSLread() or SSLwrite() is called directly. In that scenario, if the handshake fails then a fatal error will be returned in the initial function call. If SSLread()/SSLwrite() is subsequently called by the application for the same SSL object then it will succeed and the data is passed without being decrypted/encrypted directly from the SSL/TLS record layer.

In order to exploit this issue an application bug would have to be present that resulted in a call to SSLread()/SSLwrite() being issued after having already received a fatal error.

External References:

https://www.openssl.org/news/secadv/20171207.txt

If an X.509 certificate has a malformed IPAddressFamily extension, OpenSSL could do a one-byte buffer overread. The most likely result would be an erroneous display of the certificate in text format.

External References:

https://www.openssl.org/news/secadv/20170828.txt

References:

https://github.com/openssl/openssl/pull/4276

Affected versions of debug are vulnerable to regular expression denial of service when untrusted user input is passed into the o formatter.

As it takes 50,000 characters to block the event loop for 2 seconds, this issue is a low severity issue.

This was later re-introduced in version v3.2.0, and then repatched in versions 3.2.7 and 4.3.1.

Recommendation

Version 2.x.x: Update to version 2.6.9 or later. Version 3.1.x: Update to version 3.1.0 or later. Version 3.2.x: Update to version 3.2.7 or later. Version 4.x.x: Update to version 4.3.1 or later.