cocagne pysrp _ctsrp.py calculate_x information exposure

Root

Cause

A problematic vulnerability has been identified in cocagne pysrp, a Python implementation of the Secure Remote Password (SRP) protocol, affecting versions up to 1.0.16. The issue resides in the calculate_x function of the srp/_ctsrp.py file, where manipulation leads to information exposure through a discrepancy. The exact nature of the manipulation is not specified in the available references, but it likely involves a flaw in the computation or handling of the SRP proof-of-possession value that leaks subtle behavioral differences [1].

Exploitation

Vector

An attacker positioned as either a client or server in the SRP authentication exchange could potentially exploit this vulnerability. The attack requires network access to perform the SRP protocol handshake. No specific authentication is needed prior to exploitation, as the flaw occurs during the authentication challenge itself. The discrepancy likely manifests as a timing side-channel or a distinguishable error condition that reveals information about the secret parameters [1][2].

Impact

Successful exploitation leads to information exposure, which could allow an attacker to deduce sensitive cryptographic values, such as the password verifier or the user's password, over repeated interactions. This undermines the security guarantees of the SRP protocol, which is designed for password-based mutual authentication without revealing secrets [2]. The vulnerability is classified as problematic with a CVSS vector not yet fully provided, indicating it can lead to partial disclosure of confidential information [1].

Mitigation

The vulnerability is fixed in version 1.0.17 of pysrp, with the patch identifier dba52642f5e95d3da7af1780561213ee6053195f. Users are strongly advised to upgrade to this version or later. The Python Package Index (PyPI) advisory database also records this under PYSEC-2022-43014, confirming the resolution [1][3][4].