Vulnerability details

python-cryptography is a package designed to expose cryptographic primitives and recipes to Python developers. In versions 42.0.0 through 48.0.0, when resolving invalid certificate chains that include duplicate copies of self-signed certificates, the processing recursively invokes the same candidate, leading to an exponential blowup. Although the limitation that the chain depth cannot exceed a specified maximum depth prevents unbounded recursion and guarantees termination, an attacker-controlled certificate chain can lead the processing to easily take more than 5s to reject in testing. This amplification could form the basis for a resource exhaustion denial of service attack. The core issue arises in the recursive nature of build_chain_inner, which does not de-duplicate against previously analyzed candidates. As the correctness of validation is not affected, the integrity of a system cannot be compromised through this vector, only its availability. This issue is fixed in 49.0.0.

• https://github.com/pyca/cryptography/pull/14960 x_refsource_MISC
• https://github.com/pyca/cryptography/commit/3763aa79b x_refsource_MISC
• https://github.com/pyca/cryptography/commit/4a12cf49675a184e47f912b00b04f3a629283582 x_refsource_MISC
• https://github.com/pypa/advisory-database/tree/main/vulns/cryptography/PYSEC-2026-3553.yaml x_refsource_MISC
• https://github.com/pyca/cryptography/security/advisories/GHSA-jwv3-5hgf-82ww x_refsource_CONFIRM