CVE-2020-26263: RSA weakness in tslite-ng
(updated )
The code that performs decryption and padding check in RSA PKCS#1 v1.5 decryption is data dependant. In particular, code in current (as of 0.8.0-alpha38) master https://github.com/tlsfuzzer/tlslite-ng/blob/0812ed60860fa61a6573b2c0e18771414958f46d/tlslite/utils/rsakey.py#L407-L441 and code in 0.7.5 branch https://github.com/tlsfuzzer/tlslite-ng/blob/acdde3161124d6ae37c506b3476aea9996d12e97/tlslite/utils/rsakey.py#L394-L425 has multiple ways in which it leaks information (for one, it aborts as soon as the plaintext doesn’t start with 0x00, 0x02) about the decrypted ciphertext (both the bit length of the decrypted message as well as where the first unexpected byte lays).
All TLS servers that enable RSA key exchange as well as applications that use the RSA decryption API directly are vulnerable.
All previous versions of tlslite-ng are vulnerable.
References
- github.com/advisories/GHSA-wvcv-832q-fjg7
- github.com/pypa/advisory-database/tree/main/vulns/tlslite-ng/PYSEC-2020-143.yaml
- github.com/tlsfuzzer/tlslite-ng
- github.com/tlsfuzzer/tlslite-ng/commit/c28d6d387bba59d8bd5cb3ba15edc42edf54b368
- github.com/tlsfuzzer/tlslite-ng/pull/438
- github.com/tlsfuzzer/tlslite-ng/pull/439
- github.com/tlsfuzzer/tlslite-ng/security/advisories/GHSA-wvcv-832q-fjg7
- nvd.nist.gov/vuln/detail/CVE-2020-26263
- pypi.org/project/tlslite-ng
- securitypitfalls.wordpress.com/2018/08/03/constant-time-compare-in-python
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