# CVE-2026-119196: pyasn1: Quadratic CPU consumption in constructed BIT STRING decoding

CVE-2026-119196 is fixed in pyasn1 on 1 platform by DEBIAN-CVE-2026-119196 (version 0.6.5-1), released November 3, 2026. It is not reported as exploited. Patch Radar priority: High.

- Web page: https://patchblox.com/security/cve/CVE-2026-119196
- Priority: High
- CVSS: 7.5 (Important)
- EPSS: 0.0043
- CISA KEV: not listed
- Exploited (vendor report): no
- Publicly disclosed: no
- Published: Oct 29, 2026
- Weakness: Inefficient Algorithmic Complexity
- Vendor advisory: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-119196

## Description

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.

## Where it's fixed

| Platform | Product | Fixed in | Fix | Released |
|---|---|---|---|---|
| Linux | pyasn1 Debian 14 | 0.6.5-1 | [DEBIAN-CVE-2026-119196](https://patchblox.com/security/data/fix/linux/debian-cve-2026-119196.md) | Nov 3, 2026 |

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Data as of 2026-11-09T01:18:40Z UTC. Source: Patchblox Patch Radar (https://patchblox.com/security/patch-radar). Patchblox finds out-of-date software on Windows, macOS and Linux and updates it through release rings: https://patchblox.com/demo

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