Executive brief
wolfSSL is a cryptographic library used to secure communications in embedded devices and applications. A flaw in its signature verification process allows an attacker to bypass security checks by providing a specially crafted digital signature. This could allow an unauthorized party to impersonate a legitimate user or device and send forged messages that appear authentic, potentially leading to unauthorized access or data manipulation.
Technical details
The vulnerability exists in the ECCSI signature verifier function `wc_VerifyEccsiHash` within wolfSSL. The function decodes the `r` and `s` scalars from the signature blob using `mp_read_unsigned_bin` but fails to verify that these values lie within the required range of `[1, q-1]`. By exploiting this lack of bounds checking, an attacker can craft a forged signature that verifies successfully against any message for any identity using only publicly-known constants. This is classified as improper verification of a cryptographic signature (CWE-347). The issue is addressed in wolfSSL version 5.9.1.
Affected products
- wolfSSL wolfSSL up to (excluding) 5.9.1
Timeline
- 2026-03-30: other: Fix development initiated in GitHub pull request 10102
- 2026-04-06: patched: Fix merged into master branch
- 2026-04-10: advisory: CVE-2026-5466 published