CVE-2026-23490: pyasn1 memory exhaustion DoS in OID decoder

Executive brief

A denial-of-service vulnerability exists in the pyasn1 library, which is used to handle ASN.1 data in various Python applications. By sending a specially crafted, malformed data packet (such as a malicious security certificate), an attacker can cause the application to consume excessive amounts of memory. This can lead to system crashes, service outages, or unresponsive applications in environments like LDAP servers and secure web endpoints.

Technical details

A Denial-of-Service (DoS) vulnerability exists in pyasn1 v0.6.1 due to improper handling of RELATIVE-OID values during BER/DER decoding. The root cause is an integer handling issue in the decoder component where malformed RELATIVE-OID values containing excessive continuation octets lead to massive memory allocation. An unauthenticated remote attacker can exploit this by providing a crafted ASN.1 structure (e.g., within an X.509 certificate or LDAP request) that the library attempts to decode. This results in memory exhaustion and process termination. The issue is addressed in version 0.6.2 by implementing limits on the allowed bytes in the decoder.

Affected products

• pyasn1 pyasn1 0.6.1

Timeline

• 2026-01-16: advisory: GitHub Advisory GHSA-63vm-454h-vhhq published
• 2026-01-16: patched: Version 0.6.2 released

References

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