CVE-2025-66506: Fulcio allocates excessive memory during token parsing

December 5, 2025

Function identity.extractIssuerURL currently splits (via a call to strings.Split) its argument (which is untrusted data) on periods.

As a result, in the face of a malicious request with an (invalid) OIDC identity token in the payload containing many period characters, a call to extractIssuerURL incurs allocations to the tune of O(n) bytes (where n stands for the length of the function’s argument), with a constant factor of about 16. Relevant weakness: CWE-405: Asymmetric Resource Consumption (Amplification)

Details See identity.extractIssuerURL

Impact Excessive memory allocation

References

github.com/advisories/GHSA-f83f-xpx7-ffpw
github.com/sigstore/fulcio
github.com/sigstore/fulcio/commit/765a0e57608b9ef390e1eeeea8595b9054c63a5a
github.com/sigstore/fulcio/security/advisories/GHSA-f83f-xpx7-ffpw
nvd.nist.gov/vuln/detail/CVE-2025-66506

Code Behaviors & Features

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