CVE-2026-119196

pyasn1 is a generic ASN.1 library for Python. Prior to 0.6.5, constructed BIT STRING decoding repeatedly shifts and copies the complete bit value accumulated from earlier fragments. Attacker-controlled BER or CER input contains many constructed BIT STRING fragments; schema-driven DER also accepts a definite-length constructed BIT STRING. BitStringPayloadDecoder repeatedly calls BitString.fromOctetString with the prior bitString as prepend, shifting an ever-growing SizedInteger for each fragment and causing quadratic work. Large fragmented values can exhaust CPU during decode() without requiring later conversion or formatting. This issue is fixed in version 0.6.5.

• CWE-407

• https://github.com/pyasn1/pyasn1/commit/73ba7b043cc7e92cb37f16f2c955bff93b0e6f6c
• https://github.com/pyasn1/pyasn1/pull/132
• https://github.com/pyasn1/pyasn1/releases/tag/v0.6.5
• https://github.com/pyasn1/pyasn1/security/advisories/GHSA-2qm8-x737-gmw5

Published

Oct 29, 2026

Last Modified

Oct 30, 2026

Status

Awaiting Analysis

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