CVE-2020-26263

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.