CVE-2026-69249: python-cryptography Exponential Path-Building Vulnerability Due to Duplicate Self-Signed Intermediates
Summary
CVE-2026-69249: python-cryptography: Duplicate self-signed intermediates can cause exponential path-building. Affects cryptography versions < 49.0.0. Fixed in 49.0.0. How to fix ↓
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Background
The python-cryptography library is a widely used package in Python for cryptographic operations, including the creation and verification of certificates. It provides essential functionalities for secure communications and data protection. However, it is susceptible to a vulnerability that can lead to denial of service through resource exhaustion when handling invalid certificate chains containing duplicate self-signed certificates.
Vulnerability Detail
The vulnerability arises from the recursive nature of the 'build_chain_inner' function, which does not de-duplicate previously analyzed candidates. This oversight allows an attacker to craft a certificate chain that causes the processing to recursively invoke the same candidate, leading to an exponential increase in processing time. Although the maximum chain depth limits recursion, an attacker-controlled certificate chain can still result in significant delays, potentially exceeding 5 seconds to reject. This amplification can be exploited to launch a denial of service attack, affecting the availability of systems relying on this library.
How To Fix
Latest published version: 50.0.2 as of 22 Oct 2026
pip install --upgrade "cryptography==50.0.2"Upgrading to it may include breaking changes; the version below is the minimum fixed release for this vulnerability.
If you need the minimum change
49.0.0
This is the first release that contains the fix.
pip install --upgrade "cryptography==49.0.0"Tip — Not sure which version your app runs? Vulert can match this fix to it. Scan free →
Workaround
A temporary workaround involves modifying the code to track valid issuers and skip those that have already been seen. Below is an example of how to implement this in the 'build_chain_inner' function:
let mut seen_valid_issuers = Vec::<&VerificationCertificate<'chain, B>>::new();
for issuing_cert_candidate in self.potential_issuers(working_cert) {
if seen_valid_issuers.contains(&issuing_cert_candidate) {
continue;
}
seen_valid_issuers.push(issuing_cert_candidate);
match self.build_chain_inner(
issuing_cert_candidate,
// Additional parameters...
) {
// Handle result...
}
}
Conclusion
The CVE-2026-69249 vulnerability in the python-cryptography library poses a significant risk of denial of service due to exponential path-building from duplicate self-signed intermediates. It is crucial to update to version 49.0.0 or later to mitigate this risk effectively. Additionally, users can utilize Vulert to monitor their applications for vulnerabilities.
See every vulnerability recorded for cryptography →
FAQ
CVE-2026-69249 is a vulnerability in the python-cryptography library that allows for denial of service through exponential path-building when processing invalid certificate chains with duplicate self-signed certificates.
If your application uses the python-cryptography library and processes certificate chains, it may be susceptible to denial of service attacks, leading to significant delays in processing time.
The CVSS score of this vulnerability is 8.7, indicating a high severity level.
You can use Vulert, which monitors and alerts for open-source vulnerabilities in real-time. You can check your application against this vulnerability using the Vulert playground without any signup.
If immediate updates are not possible, consider implementing the provided workaround to mitigate the risk until you can upgrade to the patched version.
References
Related vulnerabilities
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