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

Source: https://junglewise.ai/threats/cve-2026-5466-wolfssl-improper-signature-verification-in-eccsi-wc  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-04-10. Updated: 2026-05-10  
License: CC BY 4.0 with a link back

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](https://junglewise.ai/threats/technologies/wolfssl). Vendors: [Wolfssl](https://junglewise.ai/threats/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](https://github.com/wolfssl/wolfssl/pull/10102)

## Related threats

- [wolfSSL certificate validation bypass in ConfirmNameConstraints()](https://junglewise.ai/threats/cve-2026-95208-an-issue-in-the-confirmnameconstraints-function-wolfcrypt-src-asn)
- [wolfSSL revocation check bypass with OCSP and CRL](https://junglewise.ai/threats/cve-2026-94417-when-an-application-enables-both-ocsp-and-crl-revocation-checking)
- [wolfSSL TLS 1.2 ChangeCipherSpec message ordering bypass](https://junglewise.ai/threats/cve-2026-93304-a-d-tls-1-2-client-can-accept-a-changecipherspec-message-before)
- [wolfSSL MatchTrustedPeer public key validation bypass](https://junglewise.ai/threats/cve-2026-93302-matchtrustedpeer-ignores-the-public-key-used-leading-to-forged-ca)
- [wolfSSL TLS authentication bypass in Raw Public Key handling](https://junglewise.ai/threats/cve-2026-89136-when-using-rpk-raw-public-key-the-client-side-of-a-tls-1-2-1-3)