GHSA-m4p7-r5rc-7g4j: pyasn1 (CVE-2026-59884)

Package	Ecosystem	Affected	Fixed in
pyasn1	PyPI	<0.6.4	0.6.4

Machine-written summary

Summary written by Claude Haiku from the source advisory. Not reviewed by a person.

Versions of pyasn1 before 0.6.4 are affected by a denial-of-service flaw in the BER, CER and DER decoders. The decoder accepts long-form tag IDs of unbounded length, so a crafted input can consume a large amount of CPU time, and on Python 3.11 and later it can raise an unhandled ValueError instead of the documented PyAsn1Error. An attacker needs only to supply crafted BER, CER or DER input to an application that decodes untrusted data. Upgrade to pyasn1 0.6.4, which limits long-form tag IDs to 20 octets. Until then, limit the size of untrusted input before passing it to decode().

Written 4 Nov 2026.

Not analysed yet

We haven’t published our analysis of this Advisory yet. Once a person has reviewed it, this page will say what’s vulnerable, what has to be true for your app to be affected, and how to check.

Severity and exploitation

Score	Rating	CVSS	Vector	Source
7.5	High	3.1	CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H	CNA (GitHub_M)

CISA KEV Not listed.
EPSS 0.0062, the 50th percentile, on 15 Nov 2026: FIRST’s estimate of the chance of exploitation in the next 30 days.

Timeline

31 Oct 2026, 14:29 UTC First seen by agentprime
31 Oct 2026, 14:29 UTC Confirmed by OSV

Sources

Facts on this page come from the GitHub Advisory Database (CC-BY 4.0), OSV and the other sources listed, as published. We don’t reproduce full advisory descriptions, which can contain exploit code.