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)
Published · last modified .
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.
EPSS exploit prediction
EPSS: 0.006 (48.9th percentile), scored .
Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 49th percentile — 48.9% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.
EPSS over last 30 days · oldest: 0.006 · newest: 0.006 · change: 0.000
Affected products
- Pyasn1 — versions < 0.6.4
Weakness classification (CWE)
References
- github.com/pyasn1/pyasn1/commit/628e36ecbb5277a3f01572ce418ef54271b165a5 (Patch)
- github.com/pyasn1/pyasn1/releases/tag/v0.6.4 (Release Notes)
- github.com/pyasn1/pyasn1/security/advisories/GHSA-m4p7-r5rc-7g4j (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.