UBUNTU-CVE-2026-119194: High severity ubuntu/pyasn1 vulnerability
pyasn1 is a generic ASN.1 library for Python. From 0.3.3 until 0.6.5, schemaless container decoding stores every decoded component's TagSet in a growing set even though only one-versus-multiple tag types must be distinguished. Attacker-controlled BER, CER, or DER input contains many distinct long tag IDs whose TagSet hashes collide. Each later set insertion compares against an increasing number of earlier colliding tags in ConstructedPayloadDecoderBase.decodeComponentsSchemaless, producing quadratic CPU work while decoded values and order remain valid. Repeated inputs can exhaust decoder CPU and reduce service availability. This issue is fixed in version 0.6.5.
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
- Upgrade
Upgrade
pyasn1to a version that resolves this vulnerability.Fixed in 0.6.5
Event History
Frequently Asked Questions
Who is exposed to this denial-of-service issue?
Applications using affected pyasn1 versions that decode attacker-controlled BER, CER, or DER data are exposed. An unauthenticated remote attacker can trigger the issue where such input is accepted over the network.
What does an attacker need to send?
The attacker needs specially crafted BER, CER, or DER input containing many distinct long tag IDs whose TagSet hashes collide. No privileges or user interaction are required.
What is the impact of successful exploitation?
Processing the crafted input causes quadratic CPU work during schemaless container decoding. Repeated requests can exhaust decoder CPU and reduce service availability, while decoded values and ordering remain valid.
Which versions are affected and what fixes it?
The issue affects pyasn1 versions from 0.3.3 through 0.6.5. The issue is fixed in version 0.6.5.