CVE-2020-26263
Description
tlslite-ng is an open source python library that implements SSL and TLS cryptographic protocols. In tlslite-ng before versions 0.7.6 and 0.8.0-alpha39, the code that performs decryption and padding check in RSA PKCS#1 v1.5 decryption is data dependant. In particular, the code has multiple ways in which it leaks information about the decrypted ciphertext. It aborts as soon as the plaintext doesn't start with 0x00, 0x02. All TLS servers that enable RSA key exchange as well as applications that use the RSA decryption API directly are vulnerable. This is patched in versions 0.7.6 and 0.8.0-alpha39. Note: the patches depend on Python processing the individual bytes in side-channel free manner, this is known to not the case (see reference). As such, users that require side-channel resistance are recommended to use different TLS implementations, as stated in the security policy of tlslite-ng.
Predictions
Heuristic predictions, AS-IS, for prioritization only.
Mitigations
No mitigations published for this CVE yet.
The vendor-content worker queues fetches as references arrive (check back in a few minutes). Or — if you've already worked around this in production — publish your fix to the community-verified tier.
✚ Propose a mitigation on Community → Mitigations published via the community go through AI scoring + 2 human reviewers + 7-day silent objection window before landing here withsource_tier=community-verified.
Package impact
| Ecosystem | Package | Vulnerable | Fixed |
|---|---|---|---|
| PyPI | tlslite-ng | <0.7.6 | 0.7.6 |
| PyPI | tlslite-ng | <c28d6d387bba59d8bd5cb3ba15edc42edf54b368||<0.7.6 | c28d6d387bba59d8bd5cb3ba15edc42edf54b368 |
References
- https://github.com/tlsfuzzer/tlslite-ng/security/advisories/GHSA-wvcv-832q-fjg7
- https://nvd.nist.gov/vuln/detail/CVE-2020-26263
- https://github.com/tlsfuzzer/tlslite-ng/pull/438
- https://github.com/tlsfuzzer/tlslite-ng/pull/439
- https://github.com/tlsfuzzer/tlslite-ng/commit/c28d6d387bba59d8bd5cb3ba15edc42edf54b368
- https://github.com/pypa/advisory-database/tree/main/vulns/tlslite-ng/PYSEC-2020-143.yaml
- https://github.com/tlsfuzzer/tlslite-ng
- https://pypi.org/project/tlslite-ng
- https://securitypitfalls.wordpress.com/2018/08/03/constant-time-compare-in-python
- https://pypi.org/project/tlslite-ng/
- https://securitypitfalls.wordpress.com/2018/08/03/constant-time-compare-in-python/
Community-verified mitigations for this CVE will appear above when contributors publish them.
Verify integrity in audit chain (admin only). AS-IS.