CVE-2025-29780 Post-Quantum Secure Feldman's Verifiable Secret Sharing has Timing Side-Channels in Matrix Operations
Timing side-channels in matrix operations allow attackers to recover secret keys from the Verifiable Secret Sharing scheme.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- None listed
What is CVE-2025-29780?
CVE-2025-29780 is a medium-severity vulnerability in DavidOsipov PostQuantum-Feldman-VSS, published on 14 Mar 2025. It can only be exploited from the same machine or local network, with no action from the victim.
Official description
Post-Quantum Secure Feldman's Verifiable Secret Sharing provides a Python implementation of Feldman's Verifiable Secret Sharing (VSS) scheme. In versions 0.8.0b2 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 extract secret information through statistical analysis of execution times, though practical exploitation would require significant expertise and controlled execution environments. Successful exploitation of these timing side-channels could allow an attacker to recover secret keys or other sensitive information protected by the VSS scheme. This could lead to a complete compromise of the shared secret. As of time of publication, no patched versions of Post-Quantum Secure Feldman's Verifiable Secret Sharing exist, but other mitigations are available. As acknowledged in the library's documentation, these vulnerabilities cannot be adequately addressed in pure Python. In the short term, consider using this library only in environments where timing measurements by attackers are infeasible. In the medium term, implement your own wrappers around critical operations using constant-time libraries in languages like Rust, Go, or C. In the long term, wait for the planned Rust implementation mentioned in the library documentation that will properly address these issues.
Which versions are affected by CVE-2025-29780?
2 open source packages ship an affected version, including PostQuantum-Feldman-VSS and postquantum-feldman-vss.
| Package | Affected | Fixed in |
|---|---|---|
PostQuantum-Feldman-VSS PyPI | All versions to 0.8.0b2 | None |
postquantum-feldman-vss PyPI | All versions to 0.8.0b2 | None |
How do I fix CVE-2025-29780?
No fix has been published for CVE-2025-29780 yet. Limit exposure of the affected software until one is available.
Is CVE-2025-29780 being exploited?
There is no known exploitation of CVE-2025-29780 in the wild and no public exploit code.
Sources
Also known as GHSA-q65w-fg65-79f4.