CVE-2026-59885
Impact
The BER/CER/DER decoders process OBJECT IDENTIFIER and RELATIVE-OID values in quadratic time relative to the number of arcs. A small crafted payload (tens of kilobytes) containing an OID with many arcs consumes seconds of CPU per decode() call, allowing denial of service in any application that decodes untrusted ASN.1 data (certificates, LDAP, SNMP, Kerberos, etc.). The corresponding encoders have the same quadratic behavior, reachable when an application re-encodes previously decoded attacker-supplied values.
The arc-size limit introduced for CVE-2026-23490 bounds the byte length of an individual arc but not the number of arcs, so it does not mitigate this issue.
Affected components
ObjectIdentifierPayloadDecoder and RelativeOIDPayloadDecoder in pyasn1/codec/ber/decoder.py; ObjectIdentifierEncoder and RelativeOIDEncoder in pyasn1/codec/ber/encoder.py. The CER and DER codecs inherit these and are equally affected.
Patches
Fixed in pyasn1 0.6.4: arc accumulation in both decoders and encoders now runs in linear time.
Workarounds
Limit the size of untrusted ASN.1 input before decoding.
CSIRTS triage
- What
- Quadratic complexity in processing OBJECT IDENTIFIER and RELATIVE-OID can lead to denial of service.
- Who is affected
- Users of pyasn1 versions before 0.5.0 are affected.
- Urgency
- This is a high urgency issue due to its high severity and potential for exploitation.
- Action
- Upgrade to pyasn1 version 0.5.0 or later.
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Exploitation outlook
- Low exploitation risk0.34% 30-day exploitation probability — currently an unlikely target, but scores change as exploit code circulates. Riskier than 26% of all EPSS-scored CVEs.
Advisory coverage (3)
- highGHSA-8ppf-4f7h-5ppj: pyasn1: Quadratic complexity in OBJECT IDENTIFIER and RELATIVE-OID processing allows deni…ghsa · 2026-07-21
- highCVE-2026-59885: pyasn1 is a generic ASN.1 library for Python. Prior to 0.6.4, the BER, CER, and DER decoders p…nvd · 2026-07-14
- highCVE-2026-59885: pyasn1: Quadratic complexity in OBJECT IDENTIFIER and RELATIVE-OID processing allows denial of…msrc · 2026-07-14
External references
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