Description
pyasn1 is a generic ASN.1 library for Python. Prior to 0.6.3, the `pyasn1` library is vulnerable to a Denial of Service (DoS) attack caused by uncontrolled recursion when decoding ASN.1 data with deeply nested structures. An attacker can supply a crafted payload containing thousands of nested `SEQUENCE` (`0x30`) or `SET` (`0x31`) tags with "Indefinite Length" (`0x80`) markers. This forces the decoder to recursively call itself until the Python interpreter crashes with a `RecursionError` or consumes all available memory (OOM), crashing the host application. This is a distinct vulnerability from CVE-2026-23490 (which addressed integer overflows in OID decoding). The fix for CVE-2026-23490 (`MAX_OID_ARC_CONTINUATION_OCTETS`) does not mitigate this recursion issue. Version 0.6.3 fixes this specific issue.
Problem types
CWE-674: Uncontrolled Recursion
Product status
References
www.openwall.com/lists/oss-security/2026/03/20/4
lists.debian.org/debian-lts-announce/2026/05/msg00001.html
github.com/...pyasn1/security/advisories/GHSA-jr27-m4p2-rc6r
github.com/...ommit/25ad481c19fdb006e20485ef3fc2e5b3eff30ef0