The vulnerability originates from a missing value barrier in the Fujisaki‑Okamoto implicit‑rejection path for several FrodoKEM variants within the liboqs library. When built with Clang 17 or later and an optimization level such as –Os, a secret‑dependent conditional load is emitted, leaving the real and rejection key paths with distinguishable cache residency patterns. This allows a local attacker who can perform repeated cache‑timing measurements to observe cache behavior differences and use the resulting oracle to recover the private key. The weakness is a timing side‑channel stemming from improper constant‑time handling of confidential data, classified under CWE‑385.

The flaw affects the open‑quantum‑safe liboqs library, versions prior to 0.16.0, when compiled with Clang 17+ at optimization levels such as –Os. The issue is present for the FrodoKEM‑640, FrodoKEM‑976 and FrodoKEM‑1344 AES and SHAKE reference variants; other algorithms in the library are not impacted by the same memory‑access pattern.

The CVSS score of 5.1 indicates medium severity. No EPSS data is available, but the vulnerability is not listed in the CISA KEV catalog, suggesting no known active exploitation. Exploitation requires a local attacker with the ability to perform precise cache‑timing measurements and a build of liboqs compiled with the vulnerable settings. The attack is therefore limited to local contexts and specialized environments, though it can lead to complete private‑key compromise if successfully carried out.