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How the Mentioned CVE Works:
During the TLS 1.2 handshake, a server can send a `CertificateRequest` message to authenticate the client. This message specifies a list of acceptable hash algorithms (digests) the client certificate’s signature must use. The vulnerability in wolfSSL occurs when the client’s TLS stack, instead of selecting a digest from the server’s authorized list, is permitted to choose any digest algorithm it supports. This allows a malicious or non-compliant client to select a cryptographically weaker digest (e.g., SHA-1) even if the server’s request explicitly required stronger ones (e.g., SHA-256 or SHA-384). By downgrading the signature hash strength, an attacker could potentially weaken the authentication security, making it easier to forge a certificate signature if the weaker hash is compromised, though the private key itself remains secure. This flaw lies in the client-side certificate selection and verification logic.
DailyCVE Form:
Platform: wolfSSL
Version: Up to 5.7.0
Vulnerability : Digest Downgrade Attack
Severity: Medium
date: 2025-11-21
Prediction: Patch 2025-12-18
What Undercode Say:
Check wolfSSL version in use strings libwolfssl.so | grep -i "wolfssl version" Simulate connection with debug (conceptual) openssl s_client -connect target:443 -tls1_2 -cert client.crt -key client.key -debug Example code snippet checking digest in CertificateVerify / In a vulnerable client, the signature algorithm from the client's certificate may not be validated against the CertificateRequest list. /
How Exploit:
An attacker operates a malicious client. During TLS 1.2 mutual authentication handshake with a vulnerable server, the attacker ignores the server’s `CertificateRequest` digest list. The attacker presents a client certificate signed with a weak algorithm (e.g., MD5). The vulnerable server accepts this weak signature, failing to enforce its stronger hash policy.
Protection from this CVE:
Update wolfSSL library. Apply patch from vendor. Enforce digest policy verification.
Impact:
Weakened client authentication. Potential for signature forgery. Man-in-the-Middle facilitation.
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Sources:
Reported By: nvd.nist.gov
Extra Source Hub:
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