Summary
Go-tuf Improperly handles multiple key IDs for the same public keys in attacker-controlled metadata
Issue
If an attacker is able to control a threshold of keys to insert the same public key more than once with different key IDs into signed, trusted metadata on a TUF repository, then go-tuf clients < 0.3.2 are susceptible to an attack where attackers can cause the same signature from the same public key to be counted more than once against the threshold of signatures because they were mistakenly distinguished due to having different key IDs.
For example, suppose that in the root metadata file, there were a threshold of 2 self-signatures required from 2 different keys $K_A$ and $K_B$ belonging to Alice and Bob respectively. Bob has either mistakenly or maliciously produced a signed a malicious version of the root metadata file where Alice's key is listed once with the keyid $SHA2_{256}(K_A)$, but his public key is listed twice, once with the keyid $SHA2_{256}(K_B)$, and the other with $SHA2_{512}(K_B)$. If Bob can convince Alice to mistakenly sign this root metadata file without noticing this error, then clients < 0.3.2 would mistakenly count the same signature from Bob twice, once with the keyid $SHA2_{256}(K_B)$, and the other with $SHA2_{512}(K_B)$.
Workarounds
Users can work around this vulnerability in previous clients by checking for and removing duplicate public keys with different key IDs (e.g., SHA2-256 and SHA2-512 hashes of the same public key) in all signed metadata on their TUF repositories.
References
- The PR fixing this issue is #369.
- The latest TUF specification advises using only SHA2-256 hashes of public keys.
- Commit b383bafd27472310a650f3733e686163a868b71a removed support for clients generating multiple key IDs for the same public key. This commit is older than the first v.0.1.0 tag for go-tuf.
- There is an outstanding issue for removing the non-standard
keyid_hash_algorithmsfield in TUF metadata which arguably led to this issue. - A more robust solution is discussed (but not necessarily recommended) in TAP 12, which suggests deduplicating public keys even more strongly on the basis of the fundamental parameters (e.g., exponents) to the cryptosystem rather than specific encodings (e.g., PEM) of public keys.
For more information
If you have any questions or comments about this advisory:
- Open an issue in go-tuf
- Email us at TUF's mailing list
- The #tuf channel on CNCF Slack.
Impact
While the impact is potentially high, the severity is low as it requires either attackers or the repository (deliberately or mistakenly respectively) to have produced such an incorrect distribution of public keys, causing clients < 0.3.2 to fall prey to this issue.
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
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. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.
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A fix is available for clients with versions >= 0.3.2.
Frequently Asked Questions
- What is GHSA-3633-5H82-39PQ? GHSA-3633-5H82-39PQ is a low-severity security vulnerability in github.com/theupdateframework/go-tuf (go), affecting versions < 0.3.2. It is fixed in 0.3.2.
- Which versions of github.com/theupdateframework/go-tuf are affected by GHSA-3633-5H82-39PQ? github.com/theupdateframework/go-tuf (go) versions < 0.3.2 is affected.
- Is there a fix for GHSA-3633-5H82-39PQ? Yes. GHSA-3633-5H82-39PQ is fixed in 0.3.2. Upgrade to this version or later.
- Is GHSA-3633-5H82-39PQ exploitable, and should I be worried? Whether GHSA-3633-5H82-39PQ 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
- What actually determines whether GHSA-3633-5H82-39PQ 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.
- How do I fix GHSA-3633-5H82-39PQ? Upgrade
github.com/theupdateframework/go-tufto 0.3.2 or later.