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Luu, T.J.

GHSA-jwv3-5hgf-82ww: python-cryptography: Duplicate self-signed intermediates can cause exponential path-building

highvulnerability

security

Source: GitHub Advisory DatabaseAugust 3, 2026CVE-2026-69249

Summary

The python-cryptography library has a vulnerability in its certificate chain validation where duplicate self-signed certificates cause exponential slowdown during processing. An attacker can craft a malicious certificate chain that takes over 5 seconds to reject, potentially causing a denial of service (resource exhaustion attack, where a system runs out of computing power by being forced to do too much work).

Solution / Mitigation

Track valid issuers in a list and skip any that have already been seen before recursing. The patch adds a `seen_valid_issuers` vector that stores previously validated issuer certificates, and checks this list before continuing the recursive chain-building process. Testing showed this fix removed the exponential slowdown while maintaining correctness, reducing processing time from 4+ seconds down to under 0.002 seconds for chains with duplicate certificates.