Is CVE-2026-5466 exploited in the wild?

No. Junglewise Threat Intelligence has no report of CVE-2026-5466 being exploited in the wild.

How severe is CVE-2026-5466?

High severity, with a CVSS score of 8.1, published 10 April 2026.

Which products and versions are affected?

wolfSSL wolfSSL up to (excluding) 5.9.1.

Is there a fix for CVE-2026-5466?

A patch was published on 2026-04-06: Fix merged into master branch Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

How is CVE-2026-5466 attacked?

It is attacked from the adjacent network, in a software library.

Am I affected by CVE-2026-5466?

Check whether you run Wolfssl. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

CVE-2026-5466: wolfSSL improper signature verification in ECCSI wc_VerifyEccsiHash

CVE-2026-5466 · Severity: high · CVSS 8.1 · Published 2026-04-10

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.

Technologies: Wolfssl. Vendors: Wolfssl.

Quick answers

Is CVE-2026-5466 exploited in the wild?: No. Junglewise Threat Intelligence has no report of CVE-2026-5466 being exploited in the wild.
How severe is CVE-2026-5466?: High severity, with a CVSS score of 8.1, published 10 April 2026.
Which products and versions are affected?: wolfSSL wolfSSL up to (excluding) 5.9.1.
Is there a fix for CVE-2026-5466?: A patch was published on 2026-04-06: Fix merged into master branch Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.
How is CVE-2026-5466 attacked?: It is attacked from the adjacent network, in a software library.
Am I affected by CVE-2026-5466?: Check whether you run Wolfssl. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

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

References

https://github.com/wolfssl/wolfssl/pull/10102

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