CVE-2023-46737

Cosign is susceptible to a denial of service by an attacker controlled registry. An attacker who controls a remote registry can return a high number of attestations and/or signatures to Cosign and cause Cosign to enter a long loop resulting in an endless data attack. The root cause is that Cosign loops through all attestations fetched from the remote registry in pkg/cosign.FetchAttestations.

The attacker needs to compromise the registry or make a request to a registry they control. When doing so, the attacker must return a high number of attestations in the response to Cosign. The result will be that the attacker can cause Cosign to go into a long or infinite loop that will prevent other users from verifying their data. In Kyvernos case, an attacker whose privileges are limited to making requests to the cluster can make a request with an image reference to their own registry, trigger the infinite loop and deny other users from completing their admission requests. Alternatively, the attacker can obtain control of the registry used by an organization and return a high number of attestations instead the expected number of attestations.

The vulnerable loop in Cosign starts on line 154 below:
https://github.com/sigstore/cosign/blob/004443228442850fb28f248fd59765afad99b6df/pkg/cosign/fetch.go#L135-L196

The l slice is controllable by an attacker who controls the remote registry.

Many cloud-native projects consider the remote registry to be untrusted, including Crossplane, Notary and Kyverno. We consider the same to be the case for Cosign, since users are not in control of whether the registry returns the expected data.

TUF's security model labels this type of vulnerability an "Endless data attack", but an attacker could use this as a type of rollback attack, in case the user attempts to deploy a patched version of a vulnerable image; The attacker could prevent this upgrade by causing Cosign to get stuck in an infinite loop and never complete.

Mitigation

The issue can be mitigated rather simply by setting a limit to the limit of attestations that Cosign will loop through. The limit does not need to be high to be within the vast majority of use cases and still prevent the endless data attack.

Crafted input forces the application to consume excessive CPU, memory, or other resources, degrading or denying service. Typical impact: denial of service.

CVE-2023-46737 has a CVSS score of 3.1 (Low). 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 (2.2.1, 1.13.2); upgrading removes the vulnerable code path.

Kodem intelligence

1. What is CVE-2023-46737? CVE-2023-46737 is a low-severity uncontrolled resource consumption vulnerability in github.com/sigstore/cosign/v2 (go), affecting versions < 2.2.1. It is fixed in 2.2.1, 1.13.2. Crafted input forces the application to consume excessive CPU, memory, or other resources, degrading or denying service.
2. How severe is CVE-2023-46737? CVE-2023-46737 has a CVSS score of 3.1 (Low). 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 packages are affected by CVE-2023-46737?
   • github.com/sigstore/cosign/v2 (go) (versions < 2.2.1)
   • github.com/sigstore/cosign (go) (versions <= 1.13.1)
4. Is there a fix for CVE-2023-46737? Yes. CVE-2023-46737 is fixed in 2.2.1, 1.13.2. Upgrade to this version or later.
5. Is CVE-2023-46737 exploitable, and should I be worried? Whether CVE-2023-46737 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-2023-46737 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-2023-46737?
   • Upgrade github.com/sigstore/cosign/v2 to 2.2.1 or later
   • Upgrade github.com/sigstore/cosign to 1.13.2 or later