GHSA-95pr-fxf5-86gv
MEDIUMCosign malicious artifacts can cause machine-wide DoS
EPSS Exploitation Probability
EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.
Blast Radius
github.com/sigstore/cosign🐹github.com/sigstore/cosign/v2Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects Go packages — download data is not available via public APIs for these ecosystems.
Description
Maliciously-crafted software artifacts can cause denial of service of the machine running Cosign, thereby impacting all services on the machine. The root cause is that Cosign creates slices based on the number of signatures, manifests or attestations in untrusted artifacts. As such, the untrusted artifact can control the amount of memory that Cosign allocates.
As an example, these lines demonstrate the problem:
This Get() method gets the manifest of the image, allocates a slice equal to the length of the layers in the manifest, loops through the layers and adds a new signature to the slice.
The exact issue is Cosign allocates excessive memory on the lines that creates a slice of the same length as the manifests.
Remediation
Update to the latest version of Cosign, where the number of attestations, signatures and manifests has been limited to a reasonable value.
Cosign PoC
In the case of this API (also referenced above):
… The first line can contain a length that is safe for the system and will not throw a runtime panic or be blocked by other safety mechanisms. For the sake of argument, let’s say that the length of m, err := s.Manifest() is the max allowed (by the machine without throwing OOM panics) manifests minus 1. When Cosign then allocates a new slice on this line: signatures := make([]oci.Signature, 0, len(m.Layers)), Cosign will allocate more memory than is available and the machine will be denied of service, causing Cosign and all other services on the machine to be unavailable.
To illustrate the issue here, we run a modified version of TestSignedImageIndex() in pkg/oci/remote:
Here, wantLayers is the number of manifests from these lines:
To test this, we want to make wantLayers high enough to not cause a memory on its own but still trigger the machine-wide OOM when a slice gets create with the same length. On my local machine, it would take hours to create a slice of layers that fulfils that criteria, so instead I modify the Cosign production code to reflect a long list of manifests:
// Get implements oci.Signatures
func (s *sigs) Get() ([]oci.Signature, error) {
m, err := s.Manifest()
if err != nil {
return nil, err
}
// Here we imitate a long list of manifests
ms := make([]byte, 2600000000) // imitate a long list of manifests
signatures := make([]oci.Signature, 0, len(ms))
panic("Done")
//signatures := make([]oci.Signature, 0, len(m.Layers))
for _, desc := range m.Layers {
With this modified code, if we can cause an OOM without triggering the panic("Done"), we have succeeded.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐹Go | github.com/sigstore/cosign | all versions | No fix |
| 🐹Go | github.com/sigstore/cosign/v2 | all versions | 2.2.4 |
Research use only. For defensive security, authorized penetration testing, and academic research only. Never execute exploit code against systems without explicit written authorization.
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for github.com/sigstore/cosign. O3's reachability analysis confirms whether the vulnerable code path is actually invoked in your application, so you act on real exposure instead of every transitive match.
Fix
No patched version of github.com/sigstore/cosign has shipped for GHSA-95pr-fxf5-86gv yet. Where your build allows, override or pin the dependency away from the vulnerable range, and apply any maintainer-recommended mitigation.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 pinpoints whether GHSA-95pr-fxf5-86gv is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.
Tailored to GHSA-95pr-fxf5-86gv. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is GHSA-95pr-fxf5-86gv in your dependencies?
O3 detects GHSA-95pr-fxf5-86gv across Go dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.