QID 983233

QID 983233: Python (pip) Security Update for tlslite-ng (GHSA-wvcv-832q-fjg7)

Security update has been released for tlslite-ng to fix the vulnerability.

Note: The preceding description block is extracted directly from the security advisory. Using automation, we have attempted to clean and format it as much as possible without introducing additional issues.

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.

CVSS V3 rated as High - 7.5 severity.

CVSS V2 rated as Medium - 5 severity.

Solution

The patches to fix it are proposed in
https://github.com/tlsfuzzer/tlslite-ng/pull/438
https://github.com/tlsfuzzer/tlslite-ng/pull/439

Note: the patches depend on Python processing the individual bytes in side-channel free manner, this is known to not be the case: https://securitypitfalls.wordpress.com/2018/08/03/constant-time-compare-in-python/
As such, users that require side-channel resistance are recommended to use different TLS implementations, as stated in the [security policy](https://github.com/tlsfuzzer/tlslite-ng/blob/master/SECURITY.md) of tlslite-ng.Workaround:
There is no way to workaround this issue.

Vendor References

GHSA-wvcv-832q-fjg7 - github.com/advisories/GHSA-wvcv-832q-fjg7

CVEs related to QID 983233

CVE-2020-26263 |

Software Advisories

Advisory ID	Software	Component	Link
GHSA-wvcv-832q-fjg7	tlslite-ng		github.com/advisories/GHSA-wvcv-832q-fjg7

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