CVE-2025-6224

Certs generated by v4 contain their private key.

Details

Background

Recently, I encountered an API in Go that’s easy to misuse: sha512.Sum384 and sha512.New384().Sum look very similar and behave very differently. https://go.dev/play/p/kDCqqoYk84k demonstrates this. I want to discuss extending static analysis to detect this case with the go community, but before I do that, I want to make a best-effort pass at open-source projects to fix the existing bugs. I figured that if there were any vulnerabilities out there, they would be easy to find once that discussion begins, so it’s better to address them early.

This work is a hobby project and has no affiliation with my employer, so I may be slow to respond due to existing commitments.

PoC

https://go.dev/play/p/vSW0U3Hq4qk

This code (cert.NewLeaf) generates certs with the SubjectKeyId set to sha512.New384().Sum(/* private */ key).

If a cert which was generated by cert.NewLeaf is transferred over the network in plaintext, as is often the case in TLS handshakes, an attacker listening on that network may sniff the cert and trivially extract the private key from it. This applies to client and server TLS certs generated by vulnerable versions of this library.

Getting the server cert and its key would only require performing a TLS handshake (with a matching SNI) with the server. At that point, the attacker could impersonate the server.

Similarly, getting the client cert and its key would require getting the client to perform a TLS handshake against an attacker-controlled server. At that point, an attacker could impersonate the client.

CVE-2025-6224 has a CVSS score of 6.5 (Medium). The vector is network-reachable, no privileges required, and user interaction required. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (4.0.4); upgrading removes the vulnerable code path.

Kodem intelligence

1. What is CVE-2025-6224? CVE-2025-6224 is a medium-severity security vulnerability in github.com/juju/utils/v4/cert (go), affecting versions <= 4.0.3. It is fixed in 4.0.4.
2. How severe is CVE-2025-6224? CVE-2025-6224 has a CVSS score of 6.5 (Medium). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
3. Which versions of github.com/juju/utils/v4/cert are affected by CVE-2025-6224? github.com/juju/utils/v4/cert (go) versions <= 4.0.3 is affected.
4. Is there a fix for CVE-2025-6224? Yes. CVE-2025-6224 is fixed in 4.0.4. Upgrade to this version or later.
5. Is CVE-2025-6224 exploitable, and should I be worried? Whether CVE-2025-6224 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
6. What actually determines whether CVE-2025-6224 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
7. How do I fix CVE-2025-6224? Upgrade github.com/juju/utils/v4/cert to 4.0.4 or later.