high7.5
CVE-2026-59884
pyasn1 BER/CER/DER decoder denial of service via unbounded long-form tag IDs
Impact
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.
Affected packages
| Ecosystem | Package | Affected | Fixed in |
|---|---|---|---|
| pip | pyasn1 | < 0.6.4 | 0.6.4 |
Affected products
| Vendor | Product | Affected versions |
|---|---|---|
| Pyasn1 | Pyasn1 | before 0.6.4 |
Weakness classification
References
- NVD record
- CVE.org record
- GitHub advisory
- https://github.com/advisories/GHSA-m4p7-r5rc-7g4j
- https://github.com/pyasn1/pyasn1/security/advisories/GHSA-m4p7-r5rc-7g4j
- https://nvd.nist.gov/vuln/detail/CVE-2026-59884
- https://github.com/pyasn1/pyasn1/commit/628e36ecbb5277a3f01572ce418ef54271b165a5
- https://github.com/pyasn1/pyasn1/releases/tag/v0.6.4
- https://github.com/pypa/advisory-database/tree/main/vulns/pyasn1/PYSEC-2026-3455.yaml