# CVE-2026-119194: pyasn1: Quadratic CPU use in schemaless BER/CER/DER container decoding

Status: published. Published: 2026-10-29. Updated: 2026-11-03.

pyasn1 is a generic ASN.1 library for Python. From 0.3.3 until 0.6.5, schemaless container decoding stores every decoded component's TagSet in a growing set even though only one-versus-multiple tag types must be distinguished. Attacker-controlled BER, CER, or DER input contains many distinct long tag IDs whose TagSet hashes collide. Each later set insertion compares against an increasing number of earlier colliding tags in ConstructedPayloadDecoderBase._decodeComponentsSchemaless, producing quadratic CPU work while decoded values and order remain valid. Repeated inputs can exhaust decoder CPU and reduce service availability. This issue is fixed in version 0.6.5.

## Remediation

- fix: pyasn1 (PyPI): OSV reports a fixed version 0.6.5. Check the advisory for supported release branches. (source: OSV GHSA-fm9c-5rcf-2q5p) — https://github.com/advisories/GHSA-fm9c-5rcf-2q5p

## Affected products and versions

- pyasn1 / pyasn1: >= 0.3.3, < 0.6.5 (affected). Source: CNA: GitHub_M
-  / pyasn1 (pyasn1): 0.3.3 (affected, PyPI); 0.3.4 (affected, PyPI); 0.3.5 (affected, PyPI); 0.3.6 (affected, PyPI); 0.3.7 (affected, PyPI); 0.4.1 (affected, PyPI); 0.4.2 (affected, PyPI); 0.4.3 (affected, PyPI); 0.4.4 (affected, PyPI); 0.4.5 (affected, PyPI); 0.4.6 (affected, PyPI); 0.4.7 (affected, PyPI); 0.4.8 (affected, PyPI); 0.5.0 (affected, PyPI); 0.5.1 (affected, PyPI); 0.6.0 (affected, PyPI); 0.6.1 (affected, PyPI); 0.6.2 (affected, PyPI); 0.6.3 (affected, PyPI); 0.6.4 (affected, PyPI); Ecosystem version events: introduced 0.3.3; fixed 0.6.5. Source: OSV GHSA-fm9c-5rcf-2q5p

## Severity and prioritization

- CVSS 3.1: 7.5 (high); CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H; source: CNA: GitHub_M

- CVSS 3.1: 7.5 (high); CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H; source: NVD: security-advisories@github.com

- CISA KEV: No listing in collected sources

- EPSS: 0.43% as of 2026-11-03; percentile 36.84%

- SSVC: exploitation poc; automatable yes; technical impact partial; source ADP: CISA-ADP

- Weaknesses: CWE-407

## Exploit evidence

- exploit: https://github.com/pyasn1/pyasn1/security/advisories/GHSA-fm9c-5rcf-2q5p (ADP: CISA-ADP)

## References

- https://github.com/pyasn1/pyasn1/security/advisories/GHSA-fm9c-5rcf-2q5p (CNA: GitHub_M; x_refsource_CONFIRM)

- https://github.com/pyasn1/pyasn1/pull/132 (CNA: GitHub_M; x_refsource_MISC)

- https://github.com/pyasn1/pyasn1/commit/a36e3a3d067148d26197a6b7221fd0e2cde9cc86 (CNA: GitHub_M; x_refsource_MISC)

- https://github.com/pyasn1/pyasn1/releases/tag/v0.6.5 (CNA: GitHub_M; x_refsource_MISC)

- https://github.com/pyasn1/pyasn1/security/advisories/GHSA-fm9c-5rcf-2q5p (ADP: CISA-ADP; exploit)

- https://github.com/pyasn1/pyasn1/commit/a36e3a3d067148d26197a6b7221fd0e2cde9cc86 (security-advisories@github.com)

- https://github.com/pyasn1/pyasn1/pull/132 (security-advisories@github.com)

- https://github.com/pyasn1/pyasn1/releases/tag/v0.6.5 (security-advisories@github.com)

- https://github.com/pyasn1/pyasn1/security/advisories/GHSA-fm9c-5rcf-2q5p (security-advisories@github.com)

- https://github.com/pyasn1/pyasn1/security/advisories/GHSA-fm9c-5rcf-2q5p (134c704f-9b21-4f2e-91b3-4a467353bcc0)

- https://github.com/advisories/GHSA-fm9c-5rcf-2q5p (OSV / GitHub Security Advisories; advisory)

- https://osv.dev/vulnerability/GHSA-fm9c-5rcf-2q5p (OSV / GitHub Security Advisories; osv)

## Provenance

- CNA: GitHub_M: https://www.cve.org/CVERecord?id=CVE-2026-119194; retrieved 2026-11-03; source updated 2026-11-03

- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-119194; retrieved 2026-11-03; source updated 2026-11-03

- OSV / GitHub Security Advisories: https://osv.dev/vulnerability/GHSA-fm9c-5rcf-2q5p; retrieved 2026-11-03; source updated 2026-10-30

- FIRST EPSS: https://api.first.org/data/v1/epss?cve=CVE-2026-119194; retrieved 2026-11-03; source updated Not reported

Revision: 1f925f454217a7824491410c4a14ca9883595f33d147f4be826f3723ebde3f30

Canonical: https://y2.dev/cve/CVE-2026-119194

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