CVE-2020-26263
In particular, the code has multiple ways in which it leaks information about the decrypted ciphertext.
Does this matter?
High impact if exploited, but EPSS currently rates exploitation as unlikely (1.50%). Schedule it in the normal patch cycle and watch for a rise in EPSS or a public exploit.
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.
- CVSS 3.1
- 7.5 HIGHCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N
- EPSS
- 1.50% probability · 73th percentile
- CISA KEV
- Not listed
- Weakness
- CWE-326
- Affected
- tlslite-ng project/tlslite-ng
- Source
- security-advisories@github.com
References
- https://github.com/tlsfuzzer/tlslite-ng/commit/c28d6d387bba59d8bd5cb3ba15edc42edf54b368Patch, Third Party Advisory
- https://github.com/tlsfuzzer/tlslite-ng/pull/438Patch, Third Party Advisory
- https://github.com/tlsfuzzer/tlslite-ng/pull/439Patch, Third Party Advisory
- https://github.com/tlsfuzzer/tlslite-ng/security/advisories/GHSA-wvcv-832q-fjg7Exploit, Patch, Third Party Advisory
- https://pypi.org/project/tlslite-ng/Product, Third Party Advisory
- https://securitypitfalls.wordpress.com/2018/08/03/constant-time-compare-in-python/Exploit, Third Party Advisory
- https://github.com/tlsfuzzer/tlslite-ng/commit/c28d6d387bba59d8bd5cb3ba15edc42edf54b368Patch, Third Party Advisory
- https://github.com/tlsfuzzer/tlslite-ng/pull/438Patch, Third Party Advisory
- https://github.com/tlsfuzzer/tlslite-ng/pull/439Patch, Third Party Advisory
- https://github.com/tlsfuzzer/tlslite-ng/security/advisories/GHSA-wvcv-832q-fjg7Exploit, Patch, Third Party Advisory
- https://pypi.org/project/tlslite-ng/Product, Third Party Advisory
- https://securitypitfalls.wordpress.com/2018/08/03/constant-time-compare-in-python/Exploit, Third Party Advisory
Source: NVD record, EPSS from FIRST.org, KEV from CISA. Refreshed daily.