Resource exhaustion in Pyasn1
CVE-2026-59884
pyasn1 is a generic ASN.1 library for Python. Prior to 0.6.4, the BER decoder shared by the CER and DER codecs parses long-form tags by accumulating continuation octets without an upper bound on the tag ID size, allowing a crafted input to force construction of an arbitrarily large integer with CPU cost growing quadratically and to trigger unhandled ValueError exceptions in Python 3.11+ error formatting paths. Any application decoding untrusted BER, CER, or DER input is affected. This issue is fixed in version 0.6.4.
Vulnerability class: DoS (Denial of Service)
EPSS: 0.003 (27.7th percentile) — read the EPSS interpretation.
CVSS v3 metric
CVSS v3 base score 7.5 (High). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H.
Affected products
- Pyasn1 — versions < 0.6.4
Weakness classification (CWE)
References
- security-advisories@github.com (Patch, x_refsource_MISC)
- security-advisories@github.com (x_refsource_MISC, Release Notes)
- security-advisories@github.com (x_refsource_CONFIRM, Third Party Advisory)
Frequently asked questions
- What is CVE-2026-59884?
- CVE-2026-59884 is a high-severity vulnerability in Pyasn1, classified under Uncontrolled Resource Consumption. CVSS score: 7.5/10. Published 2026-07-14.
- How severe is CVE-2026-59884?
- High severity. CVSS v3 base score is 7.5 out of 10.