CVE-2026-69249: python-cryptography: Duplicate self-signed intermediates can cause exponential path-building

Severity: high (CVSS 8.7 v4.0)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.3% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-08-03 · updated 2026-10-23
Weakness: CWE-400

Description

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.

Affected products

Pypi Cryptography: before 49.0.0; 0.1, 0.2, 0.2.1, 0.2.2, 0.3, 0.4 (+150) — fixed in 49.0.0
pyca cryptography: from 42.0.0, < 49.0.0

How to fix

Upgrade to a fixed version: Pypi Cryptography 49.0.0. Check the vendor advisory for mitigations.

References

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