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

Advisory record · `GHSA-f5mr-q85p-6hh6`

- **Identifiers:** `GHSA-f5mr-q85p-6hh6` · `CVE-2026-49478` · `GO-2026-5853`
- **State:** Confirmed
- **Severity:** CVSS 8.7 High
- **Critical:** No
- **Weakness (CWE):** [CWE-918](https://cwe.mitre.org/data/definitions/918.html)
- **Tags:** [Server-side request forgery (SSRF)](https://agentprime.io/advisories/tag/ssrf.md)
- **Published:** 30 Jun 2026
- **Updated:** 10 Sept 2026
- **Reviewed by a person:** No

Published by the GitHub Advisory Database at 30 Jun 2026, 18:38 UTC. agentprime has not analysed this yet, so whether it affects any app is not known.

## Affected packages

- `github.com/sigstore/fulcio` (Go): affected `<1.8.6`; fixed in `1.8.6`

## Machine-written summary

Summary written by Claude Haiku from the source advisory. Not reviewed by a person.

> Fulcio, the Go package github.com/sigstore/fulcio, versions before 1.8.6 are vulnerable. Its OIDC discovery client followed cross-host redirects, which let a malicious or compromised issuer trigger blind server-side request forgery against internal systems, substitute attacker-controlled verification keys, and leak the in-cluster Kubernetes ServiceAccount token. Upgrade to version 1.8.6, which blocks cross-host redirects and restricts token use to the matching host; no other workaround is listed.

Written 1 Nov 2026.

## Not analysed yet

We haven’t published our analysis of this Advisory yet. Once a person has reviewed it, this page will say what’s vulnerable, what has to be true for your app to be affected, and how to check.

## Severity and exploitation

- 8.7 High, CVSS 3.1: `CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:H/I:H/A:N`, from CNA (GitHub_M)

- **CISA KEV:** Not listed.
- **EPSS:** 0.0028, the 20th percentile, on 13 Nov 2026: FIRST’s estimate of the chance of exploitation in the next 30 days.

## Timeline

- 31 Oct 2026, 14:14 UTC: First seen by agentprime
- 31 Oct 2026, 14:14 UTC: [Confirmed by OSV](https://osv.dev/vulnerability/GHSA-f5mr-q85p-6hh6)

## Sources

- [GitHub Advisory Database: GHSA-f5mr-q85p-6hh6](https://github.com/advisories/GHSA-f5mr-q85p-6hh6)
- [OSV: GHSA-f5mr-q85p-6hh6](https://osv.dev/vulnerability/GHSA-f5mr-q85p-6hh6)
- <https://github.com/sigstore/fulcio/security/advisories/GHSA-f5mr-q85p-6hh6>
- <https://github.com/sigstore/fulcio>

Facts on this page come from the GitHub Advisory Database (CC-BY 4.0), OSV and the other sources listed, as published. We don’t reproduce full advisory descriptions, which can contain exploit code.

## Check whether this affects you

A Match means an installed version is in the affected range above. Most don’t affect the app; agentprime hasn’t analysed this one yet.

- With the agentprime MCP server (<https://api.agentprime.io/mcp>), ask your agent to check the project: `check_lockfile` sends a lockfile, `check_packages` a list of installed packages, and both return the Matches and the upgrades that clear them. `get_advisory` returns this record. Setup: <https://agentprime.io/mcp.md>
- In a browser: <https://agentprime.io/check/> reads your lockfile in the browser, never uploading it.
- Whether it touches your code, with file and line: the Claude Code plugin, <https://agentprime.io/plugin.md>
- As JSON: <https://api.agentprime.io/v1/advisories/GHSA-f5mr-q85p-6hh6>, or `POST https://api.agentprime.io/v1/match` with your packages (<https://agentprime.io/api.md>)

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The web page: <https://agentprime.io/advisories/GHSA-f5mr-q85p-6hh6/>. Everything for agents: <https://agentprime.io/llms.txt>.