gh cache

Author: carlospolop

src/pentesting-ci-cd/github-security/abusing-github-actions/README.md

@@ -481,6 +481,7 @@ GitHub exposes a cross-workflow cache that is keyed only by the string you suppl
 - Cache entries are shared across workflows and branches whenever the `key` or `restore-keys` match. GitHub does not scope them to trust levels.
 - Saving to the cache is allowed even when the job supposedly has read-only repository permissions, so “safe” workflows can still poison high-trust caches.
 - Official actions (`setup-node`, `setup-python`, dependency caches, etc.) frequently reuse deterministic keys, so identifying the correct key is trivial once the workflow file is public.
+- Restores are just zstd tarball extractions with no integrity checks, so poisoned caches can overwrite scripts, `package.json`, or other files under the restore path.
 
 **Mitigations**
 
@@ -806,4 +807,3 @@ An organization in GitHub is very proactive in reporting accounts to GitHub. All
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-

src/pentesting-ci-cd/github-security/abusing-github-actions/gh-actions-cache-poisoning.md

@@ -10,7 +10,10 @@ The GitHub Actions cache is global to a repository. Any workflow that knows a ca
 
 - `actions/cache` exposes both restore and save operations (`actions/cache@v4`, `actions/cache/save@v4`, `actions/cache/restore@v4`). The save call is allowed for any job except truly untrusted `pull_request` workflows triggered from forks.
 - Cache entries are identified solely by the `key`. Broad `restore-keys` make it easy to inject payloads because the attacker only needs to collide with a prefix.
+- Cache keys and versions are client-specified values; the cache service does not validate that a key/version matches a trusted workflow or cache path.
+- The cache server URL + runtime token are long-lived relative to the workflow (historically ~6 hours, now ~90 minutes) and are not user-revocable. As of late 2024 GitHub blocks cache writes after the originating job completes, so attackers must write while the job is still running or pre-poison future keys.
 - The cached filesystem is restored verbatim. If the cache contains scripts or binaries that are executed later, the attacker controls that execution path.
+- The cache file itself is not validated on restore; it is just a zstd-compressed archive, so a poisoned entry can overwrite scripts, `package.json`, or other files under the restore path.
 
 ## Example exploitation chain
 
@@ -41,6 +44,16 @@ steps:
 
 The second job now runs attacker-controlled code while holding release credentials (PyPI tokens, PATs, cloud deploy keys, etc.).
 
+## Poisoning mechanics
+
+GitHub Actions cache entries are typically zstd-compressed tar archives. You can craft one locally and upload it to the cache:
+
+```bash
+tar --zstd -cf poisoned_cache.tzstd cache/contents/here
+```
+
+On a cache hit, the restore action will extract the archive as-is. If the cache path includes scripts or config files that are executed later (build tooling, `action.yml`, `package.json`, etc.), you can overwrite them to gain execution.
+
 ## Practical exploitation tips
 
 - Target workflows triggered by `pull_request_target`, `issue_comment`, or bot commands that still save caches; GitHub lets them overwrite repository-wide keys even when the runner only has read access to the repo.
@@ -50,5 +63,7 @@ The second job now runs attacker-controlled code while holding release credentia
 ## References
 
 - [A Survey of 2024–2025 Open-Source Supply-Chain Compromises and Their Root Causes](https://words.filippo.io/compromise-survey/)
+- [The Monsters in Your Build Cache: GitHub Actions Cache Poisoning](http://adnanthekhan.com/2024/05/06/the-monsters-in-your-build-cache-github-actions-cache-poisoning/)
+- [ActionsCacheBlasting (deprecated, Cache V2) / Cacheract](https://github.com/AdnaneKhan/ActionsCacheBlasting)
 
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