CVE-2026-65634: Superlinear CPU denial of service in Erlang/OTP ASN.1 OBJECT IDENTIFIER decoder
Inefficient algorithmic complexity in the Erlang/OTP asn1 OBJECT IDENTIFIER decoder allows a remote unauthenticated attacker to cause denial of service by sending a crafted OID during the TLS handshake.
The BER OID decoder asn1rttber:decsubidentifiers/3 in lib/asn1/src/asn1rttber.erl and the equivalent PER helper asn1rttpercommon:decsubidentifiers/3 in lib/asn1/src/asn1rttpercommon.erl accumulate a base-128 subidentifier into an unbounded integer using (Av bsl 7) + H per continuation byte. Each shift and addition on the growing accumulator is linear in the number of bits already accumulated, giving quadratic total work in the size of a single subidentifier. The JER helper asn1rttjer:json2oid/1 in lib/asn1/src/asn1rttjer.erl exhibits the same class of unbounded-integer parsing when decoding a dot-separated OID from JSON. A DER-encoded OBJECT IDENTIFIER with one very large arc (approximately 262 KB of continuation bytes) consumes roughly 13 seconds of CPU on typical hardware.
The vulnerable decoder is generated into every ASN.1 module that contains an OBJECT IDENTIFIER, including OTP-PUB-KEY which is reached during X.509 certificate parsing via publickey:pkixdecodecert/2. This decoder runs before any signature or trust chain verification, so any Erlang service that parses peer TLS certificates is exposed: the default for TLS clients (which always parse the server certificate) and for mutual-TLS servers (which parse client certificates).
This vulnerability is associated with program files lib/asn1/src/asn1rttber.erl, lib/asn1/src/asn1rttpercommon.erl and lib/asn1/src/asn1rttjer.erl and program routines asn1rttber:decsubidentifiers/3, asn1rttpercommon:decsubidentifiers/3 and asn1rttjer:json2oid/1.
This issue affects OTP from OTP 17.0 before OTP 27.3.4.18, OTP 28.5.0.7, and OTP 29.1.1, corresponding to asn1 from 3.0 before 5.3.4.3, 5.4.3.1, and 5.5.2. Whether OTP before OTP 17.0, corresponding to asn1 before 3.0, is affected is unknown.
Affected Software
Event History
Frequently Asked Questions
Who is realistically exposed to this issue?
Erlang/OTP applications that parse attacker-controlled X.509 certificates during TLS handshakes are exposed because OTP-PUB-KEY contains an OBJECT IDENTIFIER decoder reached through public_key:pkix_decode_cert/2. ASN.1 modules containing OBJECT IDENTIFIER fields may also be affected when they decode untrusted BER, PER, or JER data.
What does an attacker need to exploit it?
The attacker can be remote and unauthenticated. They need to send crafted input containing an OBJECT IDENTIFIER with an extremely large base-128 subidentifier, such as a malicious OID in a certificate presented during a TLS handshake.
What is the expected operational impact?
The crafted OID causes superlinear CPU consumption while the decoder builds an unbounded integer. A DER OID with a single arc of about 262 KB of continuation bytes is reported to consume roughly 13 seconds of CPU on typical hardware, which can enable denial of service.
How can I identify potentially affected code paths?
Review whether the application accepts untrusted certificates or other untrusted ASN.1 input and invokes certificate parsing through public_key:pkix_decode_cert/2. Also identify ASN.1 modules with OBJECT IDENTIFIER fields and any use of BER, PER, or JER OID decoding on attacker-controlled data.