# CVE-2026-119196: pyasn1 quadratic CPU exhaustion in BIT STRING decoding

Source: https://junglewise.ai/threats/cve-2026-119196-pyasn1-is-a-generic-asn-1-library-for-python-prior-to-0-6-5  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-10-29. Updated: 2026-10-29  
License: CC BY 4.0 with a link back

CVE-2026-119196 · Severity: high · CVSS 7.5 · Published 2026-10-29

pyasn1 is a Python library used to parse and handle ASN.1 encoded data in applications across many domains. Attackers can send specially crafted malformed ASN.1 data with many BIT STRING fragments that cause the library to consume CPU quadratically during decoding, potentially denying service to applications relying on it. This affects any service or application that parses untrusted ASN.1 input using vulnerable versions.

Technologies: [Pyasn1](https://junglewise.ai/threats/technologies/pyasn1), [pyasn1 (PyPI)](https://junglewise.ai/threats/technologies/pypi-pyasn1). Vendors: [Pyasn1](https://junglewise.ai/threats/vendors/pyasn1), [PyPI](https://junglewise.ai/threats/vendors/pypi).

## Quick answers

**Is CVE-2026-119196 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-119196 being exploited in the wild.

**How severe is CVE-2026-119196?** High severity, with a CVSS score of 7.5, published 29 October 2026.

**Which products and versions are affected?** Pyasn1 before 0.6.5; pyasn1 (PyPI) <= 0.6.4, ECOSYSTEM:introduced=0,fixed=0.6.5.

**Is there a fix for CVE-2026-119196?** Yes. pyasn1 (PyPI): upgrade to 0.6.5 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-119196 attacked?** It is attacked over the network, in a software library.

**Am I affected by CVE-2026-119196?** Check whether you run Pyasn1 or pyasn1 (PyPI) at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## How to fix

- pyasn1 (PyPI): upgrade to 0.6.5 or later

  ```sh
  pip install "pyasn1>=0.6.5"
  ```


## Technical details

The vulnerability is a quadratic algorithmic complexity issue in constructed BIT STRING decoding. BitStringPayloadDecoder processes fragments by repeatedly calling BitString.fromOctetString with the prior bitString as a prepend parameter, causing exponential SizedInteger shifting for each fragment; attackers send many fragments via BER/CER-encoded or schema-driven DER input to trigger CPU exhaustion. Large fragmented values exhaust CPU during decode() without requiring any conversion or formatting, enabling denial of service.

## Affected products

- pyasn1 pyasn1 before 0.6.5

## Identifiers

- CVE-2026-119196
- GHSA-2qm8-x737-gmw5

## Timeline

- 2026-10-29: disclosed
- 2026-10-27: patched

## References

- [https://github.com/pyasn1/pyasn1/commit/73ba7b043cc7e92cb37f16f2c955bff93b0e6f6c](https://github.com/pyasn1/pyasn1/commit/73ba7b043cc7e92cb37f16f2c955bff93b0e6f6c)
- [https://github.com/pyasn1/pyasn1/pull/132](https://github.com/pyasn1/pyasn1/pull/132)

## Related threats

- [pyasn1 quadratic binary REAL mantissa decoding DoS](https://junglewise.ai/threats/cve-2026-119197-pyasn1-is-a-generic-asn-1-library-for-python-prior-to-0-6-5)
- [pyasn1 quadratic algorithm denial of service in ASN.1 decoding](https://junglewise.ai/threats/cve-2026-119195-pyasn1-is-a-generic-asn-1-library-for-python-prior-to-0-6-5)
- [pyasn1 quadratic CPU use in schemaless container decoding](https://junglewise.ai/threats/cve-2026-119194-pyasn1-is-a-generic-asn-1-library-for-python-from-0-3-3-until-0)
- [pyasn1 resource consumption in univ.Real float conversion](https://junglewise.ai/threats/cve-2026-59886-pyasn1-resource-consumption-in-univ-real-float-conversion)
- [pyasn1 algorithmic complexity denial of service in OID processing](https://junglewise.ai/threats/cve-2026-59885-pyasn1-algorithmic-complexity-denial-of-service-in-oid-processing)