Description

Post-Quantum Secure Feldman's Verifiable Secret Sharing provides a Python implementation of Feldman's Verifiable Secret Sharing (VSS) scheme. In versions 0.7.6b0 and prior, the `feldman_vss` library contains timing side-channel vulnerabilities in its matrix operations, specifically within the `_find_secure_pivot` function and potentially other parts of `_secure_matrix_solve`. These vulnerabilities are due to Python's execution model, which does not guarantee constant-time execution. An attacker with the ability to measure the execution time of these functions (e.g., through repeated calls with carefully crafted inputs) could potentially recover secret information used in the Verifiable Secret Sharing (VSS) scheme. The `_find_secure_pivot` function, used during Gaussian elimination in `_secure_matrix_solve`, attempts to find a non-zero pivot element. However, the conditional statement `if matrix[row][col] != 0 and row_random < min_value:` has execution time that depends on the value of `matrix[row][col]`. This timing difference can be exploited by an attacker. The `constant_time_compare` function in this file also does not provide a constant-time guarantee. The Python implementation of matrix operations in the _find_secure_pivot and _secure_matrix_solve functions cannot guarantee constant-time execution, potentially leaking information about secret polynomial coefficients. An attacker with the ability to make precise timing measurements of these operations could potentially...

Classification

CVE ID: CVE-2025-29780

CVSS Base Severity: MEDIUM

CVSS Base Score: 5.8

CVSS Vector: CVSS:4.0/AV:L/AC:H/AT:P/PR:L/UI:N/VC:H/VI:L/VA:N/SC:N/SI:N/SA:N

Affected Products

Vendor: DavidOsipov

Product: PostQuantum-Feldman-VSS

Exploit Prediction Scoring System (EPSS)

EPSS Score: 0.06% (probability of being exploited)

EPSS Percentile: 15.79% (scored less or equal to compared to others)

EPSS Date: 2025-04-12 (when was this score calculated)

References

https://nvd.nist.gov/vuln/detail/CVE-2025-29780
https://github.com/DavidOsipov/PostQuantum-Feldman-VSS/security/advisories/GHSA-q65w-fg65-79f4
https://en.wikipedia.org/wiki/Side-channel_attack
https://www.rambus.com/wp-content/uploads/2015/08/TimingAttacks.pdf

Timeline