Описание
pyasn1 BER/CER/DER decoder denial of service via unbounded long-form tag IDs
Impact
The BER decoder (shared by the CER and DER codecs) parses long-form tags by accumulating continuation octets in a loop with no upper bound on the size of the tag ID. A crafted input can force the decoder to build an arbitrarily large integer, with CPU cost growing quadratically in input size — a ~1 MB input consumes over a minute of CPU. On Python 3.11+, the oversized tag ID can also trigger an unhandled ValueError (integer string conversion limit) while the decoder formats error messages, violating the documented PyAsn1Error contract and potentially bypassing caller error handling.
Any application decoding untrusted BER/CER/DER input is affected.
Affected components
pyasn1.codec.ber.decoder—decode()andStreamingDecoderpyasn1.codec.cer.decoderandpyasn1.codec.der.decoder, which inherit the same tag parsingpyasn1.type.tag—Tag/TagSetreprs could raiseValueErrorwhen rendering oversized tag IDs (reachable through decoder error paths)
The encoders and the pyasn1.codec.native codec are not affected.
Patches
Fixed in 0.6.4. Long-form tag IDs are now limited to 20 octets (140-bit tag IDs, matching the existing OID arc limit); oversized tags are rejected with PyAsn1Error. Tag ID rendering in reprs and error messages was additionally hardened against the interpreter's integer-to-string conversion limit.
Workarounds
Bound the size of untrusted input passed to decode() before calling it.
Ссылки
- 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
Пакеты
pyasn1
< 0.6.4
0.6.4
Связанные уязвимости
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.
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.
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.
pyasn1 BER/CER/DER decoder denial of service via unbounded long-form tag IDs
pyasn1 is a generic ASN.1 library for Python. Prior to 0.6.4, the BER ...