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GHSA-cq38-jh5f-37mq
No affected components available
Impact
sigstore-go is susceptible to a denial of service attack when a verifier is provided a maliciously crafted Sigstore Bundle containing large amounts of verifiable data, in the form of signed transparency log entries, RFC 3161 timestamps, and attestation subjects. The verification of these data structures is computationally expensive. This can be used to consume excessive CPU resources, leading to a denial of service attack. TUF's security model labels this type of vulnerability an "Endless data attack," and can lead to verification failing to complete and disrupting services that rely on sigstore-go for verification.
The vulnerable loops are in the verification functions in the package github.com/sigstore/sigstore-go/pkg/verify. The first is the DSSE envelope verification loop in verifyEnvelopeWithArtifact, which decodes all the digests in an attestation can be found here:
https://github.com/sigstore/sigstore-go/blob/725e508ed4933e6f5b5206e32af4bbe76f587b54/pkg/verify/signature.go#L183-L193
The next loop is in the VerifyArtifactTransparencyLog function, which verifies all the signed entries in a bundle:
https://github.com/sigstore/sigstore-go/blob/725e508ed4933e6f5b5206e32af4bbe76f587b54/pkg/verify/tlog.go#L74-L178
The next loop is the VerifyTimestampAuthority function, which verifies all the RFC 3161 timestamps in a bundle:
https://github.com/sigstore/sigstore-go/blob/725e508ed4933e6f5b5206e32af4bbe76f587b54/pkg/verify/tsa.go#L59-L68
Patches
This vulnerability is addressed with sigstore-go 0.6.1, which adds hard limits to the number of verifiable data structures that can be processed in a bundle. Verification will fail if a bundle has data that exceeds these limits. The limits are:
- 32 signed transparency log entries
- 32 RFC 3161 timestamps
- 1024 attestation subjects
- 32 digests per attestation subject
These limits are intended to be high enough to accommodate the vast majority of use cases, while preventing the verification of maliciously crafted bundles that contain large amounts of verifiable data.
Workarounds
The best way to mitigate the risk is to upgrade to sigstore-go 0.6.1 or later. Users who are vulnerable but unable to quickly upgrade may consider adding manual bundle validation to enforce limits similar to those in the referenced patch prior to calling sigstore-go's verification functions.
The vulnerability can be exploited over the network without needing physical access. It is difficult for an attacker to exploit this vulnerability and may require special conditions. An attacker does not need any special privileges or access rights. The attacker needs the user to perform some action, like clicking a link. The impact is confined to the system where the vulnerability exists. There is a low impact on the availability of the system.
Limited exploitation activity has been observed. Close monitoring and planned remediation are recommended.
The exploit probability is very low. The vulnerability is unlikely to be exploited in the next 30 days.
We did not find any exploit available. Neither in GitHub repositories nor in the Exploit-Database.
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