Update cache poisoning queries for the new cache-mode syntax https://github.blog/changelog/2026-09-10-control-github-actions-cache-access-with-cache-mode/

Author: JarLob

actions/ql/lib/change-notes/2026-09-17-cache-mode.md

@@ -0,0 +1,5 @@
+---
+category: feature
+---
+* Added `Workflow.getCacheMode()` and `Job.getCacheMode()` to read explicitly declared cache modes. The `hasDefaultBranchCacheWriteAccess` predicate now accounts for these modes, job overrides, and explicit caller limits in reusable workflows.
+* `runsOnDefaultBranch` now includes unfiltered branch pushes and `pull_request` `closed` events that may refer to a merge into the default branch, while excluding tag-only pushes.

actions/ql/lib/codeql/actions/Ast.qll

@@ -104,6 +104,9 @@ class Workflow extends AstNode instanceof WorkflowImpl {
 
   Permissions getPermissions() { result = super.getPermissions() }
 
+  /** Gets the explicitly declared cache mode for this workflow, if any. */
+  string getCacheMode() { result = super.getCacheMode() }
+
   Strategy getStrategy() { result = super.getStrategy() }
 
   On getOn() { result = super.getOn() }
@@ -200,6 +203,9 @@ abstract class Job extends AstNode instanceof JobImpl {
 
   Permissions getPermissions() { result = super.getPermissions() }
 
+  /** Gets the explicitly declared cache mode for this job, if any. */
+  string getCacheMode() { result = super.getCacheMode() }
+
   Strategy getStrategy() { result = super.getStrategy() }
 
   string getARunsOnLabel() { result = super.getARunsOnLabel() }

actions/ql/lib/codeql/actions/ast/internal/Ast.qll

@@ -494,6 +494,9 @@ class WorkflowImpl extends AstNodeImpl, TWorkflowNode {
   /** Gets the permissions granted to this workflow. */
   PermissionsImpl getPermissions() { result.getNode() = n.lookup("permissions") }
 
+  /** Gets the explicitly declared cache mode for this workflow, if any. */
+  string getCacheMode() { result = n.lookup("cache-mode").(YamlString).getValue() }
+
   /** Gets the trigger event that starts this workflow. */
   override EventImpl getATriggerEvent() { this.getOn().getAnEvent() = result }
 
@@ -923,6 +926,9 @@ class JobImpl extends AstNodeImpl, TJobNode {
   /** Gets the permissions for this job. */
   PermissionsImpl getPermissions() { result.getNode() = n.lookup("permissions") }
 
+  /** Gets the explicitly declared cache mode for this job, if any. */
+  string getCacheMode() { result = n.lookup("cache-mode").(YamlString).getValue() }
+
   /** Gets the strategy for this job. */
   StrategyImpl getStrategy() { result.getNode() = n.lookup("strategy") }
 

actions/ql/lib/codeql/actions/security/CachePoisoningQuery.qll

@@ -10,15 +10,27 @@ string defaultBranchTriggerEvent() {
     ]
 }
 
+/**
+ * Holds if `e` can run in the default-branch cache scope.
+ * A pull request closed by a merge uses its base branch instead of its merge ref.
+ */
 predicate runsOnDefaultBranch(Event e) {
   (
     e.getName() = defaultBranchTriggerEvent() and
     not e.getName() = "pull_request_target"
     or
-    e.getName() = "push" and
-    e.getAPropertyValue("branches") = defaultBranchNames()
-    or
-    e.getName() = "pull_request_target" and
+    (
+      e.getName() = "push" and
+      (
+        e.hasProperty(["branches", "branches-ignore"])
+        or
+        not e.hasProperty(["tags", "tags-ignore"])
+      )
+      or
+      e.getName() = "pull_request_target"
+      or
+      e.getName() = "pull_request" and e.getAnActivityType() = "closed"
+    ) and
     (
       // no filtering
       not e.hasProperty("branches") and not e.hasProperty("branches-ignore")
@@ -50,17 +62,61 @@ private string defaultBranchCacheWriteEvent() {
     ]
 }
 
-private predicate eventHasDefaultBranchCacheWriteAccess(Event event) {
-  runsOnDefaultBranch(event) and event.getName() = defaultBranchCacheWriteEvent()
+private string getDeclaredCacheMode(Job job) {
+  result = job.getCacheMode()
+  or
+  not exists(job.getCacheMode()) and
+  result = job.getWorkflow().getCacheMode()
+}
+
+private predicate cacheModeIsAllowed(string mode, string inheritedMode) {
+  mode = ["read", "write", "write-only", "none"] and
+  inheritedMode = ["default", "read", "write", "write-only", "none"] and
+  (inheritedMode = ["default", "write"] or mode = ["none", inheritedMode])
+}
+
+/**
+ * Gets the effective declared cache mode, or `default` if no mode was declared in the call chain.
+ * An event's implicit default does not limit the modes a reusable workflow can request.
+ * Both the callee's workflow-level mode and its job-level modes must fit the caller's explicit limit.
+ */
+private string getEffectiveCacheMode(Job job, Event event) {
+  exists(string inheritedMode |
+    (
+      job.getWorkflow().getOn().getAnEvent() = event and
+      not event.getName() = "workflow_call" and
+      inheritedMode = "default"
+      or
+      inheritedMode =
+        getEffectiveCacheMode(job.getWorkflow().(ReusableWorkflow).getACaller(), event)
+    )
+  |
+    (
+      not exists(job.getWorkflow().getCacheMode())
+      or
+      cacheModeIsAllowed(job.getWorkflow().getCacheMode(), inheritedMode)
+    ) and
+    if exists(getDeclaredCacheMode(job))
+    then
+      result = getDeclaredCacheMode(job) and
+      cacheModeIsAllowed(result, inheritedMode)
+    else result = inheritedMode
+  )
 }
 
 /**
  * Holds if `job` can write to the cache scope of the default branch for `event`.
- * Reusable workflow jobs inherit their caller's trigger event.
+ * Job cache modes override workflow cache modes, subject to explicit limits from reusable workflow
+ * callers. Trigger-based defaults apply only if no cache mode was declared in the call chain.
  */
 predicate hasDefaultBranchCacheWriteAccess(LocalJob job, Event event) {
   job.getATriggerEvent() = event and
-  eventHasDefaultBranchCacheWriteAccess(event)
+  runsOnDefaultBranch(event) and
+  exists(string mode | mode = getEffectiveCacheMode(job, event) |
+    mode = ["write", "write-only"]
+    or
+    mode = "default" and event.getName() = defaultBranchCacheWriteEvent()
+  )
 }
 
 abstract class CacheWritingStep extends Step {

actions/ql/src/Security/CWE-349/CachePoisoningViaCodeInjection.md

@@ -1,6 +1,6 @@
 ## Overview
 
-GitHub Actions cache poisoning is a technique that allows an attacker to inject malicious content into the Action's cache from unprivileged workflow, potentially leading to code execution in privileged workflows.
+GitHub Actions cache poisoning is a technique that allows an attacker to inject malicious content into the Actions cache from an unprivileged workflow with cache-write access, potentially leading to code execution in privileged workflows.
 
 An attacker with the ability to run code in the context of the default branch (e.g. through Code Injection or Execution of Untrusted Code) can exploit this to:
 
@@ -23,7 +23,13 @@ Due to the above design, if something is cached in the context of the default br
 
 ## Recommendation
 
-1. Avoid using caching in workflows that handle sensitive operations like releases.
+Set `cache-mode: read` on workflows or jobs that process untrusted input and only need to restore
+caches, or `cache-mode: none` if they do not need cache access. These restrictions are enforced by
+the cache service. Job-level settings override workflow-level settings. Set an explicit mode on
+jobs that call reusable workflows to limit the access those workflows can request. Do not use
+`write-only` to prevent cache poisoning: it prevents restores but still permits saves.
+
+1. Avoid restoring caches in workflows that handle sensitive operations like releases. Use `cache-mode: none` to disable cache access.
 2. If caching must be used:
    - Validate restored cache contents before use.
    - Use short-lived, workflow-specific cache keys.
@@ -34,9 +40,13 @@ Due to the above design, if something is cached in the context of the default br
 
 ## Example
 
-GitHub gives workflows triggered by low-trust events, such as `issue_comment`,
+By default, GitHub gives workflows triggered by low-trust events, such as `issue_comment`,
 `pull_request_target`, and `workflow_run`, read-only access to the default branch cache scope.
-This query therefore reports only workflows whose trigger can write to that scope.
+An explicit `cache-mode: write` or `cache-mode: write-only` grants write access even for these
+triggers, while `read` and `none` prevent cache saves. Reusable workflows cannot exceed an explicit
+mode set by their caller, but can override an implicit trigger-based default.
+This query reports only jobs that can write to the default branch cache scope, accounting for
+the trigger, branch, and effective cache mode.
 
 ### Incorrect Usage
 
@@ -62,7 +72,7 @@ jobs:
 ### Correct Usage
 
 The following workflow passes the commit message through an environment variable, so the shell
-does not interpret its contents as code.
+does not interpret its contents as code. It also explicitly prevents cache saves with `cache-mode: read`.
 
 ```yaml
 name: Secure Workflow
@@ -73,6 +83,7 @@ on:
 jobs:
   build:
     permissions: {}
+    cache-mode: read
     runs-on: ubuntu-latest
     steps:
       - env:
@@ -85,4 +96,5 @@ jobs:
 
 - Adnan Khan's Blog: [The Monsters in Your Build Cache – GitHub Actions Cache Poisoning](https://adnanthekhan.com/2024/05/06/the-monsters-in-your-build-cache-github-actions-cache-poisoning/).
 - GitHub Docs: [Cache access for low-trust workflow triggers](https://docs.github.com/actions/reference/workflows-and-actions/dependency-caching#cache-access-for-low-trust-workflow-triggers).
+- GitHub Docs: [Controlling cache access with cache-mode](https://docs.github.com/actions/reference/workflows-and-actions/dependency-caching#controlling-cache-access-with-cache-mode).
 - Scribe Security Blog: [Cache Poisoning in GitHub Actions](https://scribesecurity.com/blog/github-cache-poisoning/).

actions/ql/src/Security/CWE-349/CachePoisoningViaDirectCache.md

@@ -1,6 +1,6 @@
 ## Overview
 
-GitHub Actions cache poisoning is a technique that allows an attacker to inject malicious content into the Action's cache from unprivileged workflow, potentially leading to code execution in privileged workflows.
+GitHub Actions cache poisoning is a technique that allows an attacker to inject malicious content into the Actions cache from an unprivileged workflow with cache-write access, potentially leading to code execution in privileged workflows.
 
 An attacker with the ability to run code in the context of the default branch (e.g. through Code Injection or Execution of Untrusted Code) can exploit this to:
 
@@ -23,7 +23,13 @@ Due to the above design, if something is cached in the context of the default br
 
 ## Recommendation
 
-1. Avoid using caching in workflows that handle sensitive operations like releases.
+Set `cache-mode: read` on workflows or jobs that process untrusted input and only need to restore
+caches, or `cache-mode: none` if they do not need cache access. These restrictions are enforced by
+the cache service. Job-level settings override workflow-level settings. Set an explicit mode on
+jobs that call reusable workflows to limit the access those workflows can request. Do not use
+`write-only` to prevent cache poisoning: it prevents restores but still permits saves.
+
+1. Avoid restoring caches in workflows that handle sensitive operations like releases. Use `cache-mode: none` to disable cache access.
 2. If caching must be used:
    - Validate restored cache contents before use.
    - Use short-lived, workflow-specific cache keys.
@@ -34,9 +40,13 @@ Due to the above design, if something is cached in the context of the default br
 
 ## Example
 
-GitHub gives workflows triggered by low-trust events, such as `issue_comment`,
+By default, GitHub gives workflows triggered by low-trust events, such as `issue_comment`,
 `pull_request_target`, and `workflow_run`, read-only access to the default branch cache scope.
-This query therefore reports only workflows whose trigger can write to that scope.
+An explicit `cache-mode: write` or `cache-mode: write-only` grants write access even for these
+triggers, while `read` and `none` prevent cache saves. Reusable workflows cannot exceed an explicit
+mode set by their caller, but can override an implicit trigger-based default.
+This query reports only jobs that can write to the default branch cache scope, accounting for
+the trigger, branch, and effective cache mode.
 
 ### Incorrect Usage
 
@@ -71,13 +81,16 @@ jobs:
 
 ### Correct Usage
 
-The following workflow checking out untrusted files, but the cache is scoped to the Pull Request.
+The following workflow checks out untrusted files in a pull request's isolated cache scope.
+It also explicitly prevents cache saves with `cache-mode: read`.
 
 ```yaml
 name: Secure Workflow
 on:
   pull_request:
 
+cache-mode: read
+
 jobs:
   pr-comment:
     permissions: read-all
@@ -99,4 +112,5 @@ jobs:
 
 - Adnan Khan's Blog: [The Monsters in Your Build Cache – GitHub Actions Cache Poisoning](https://adnanthekhan.com/2024/05/06/the-monsters-in-your-build-cache-github-actions-cache-poisoning/).
 - GitHub Docs: [Cache access for low-trust workflow triggers](https://docs.github.com/actions/reference/workflows-and-actions/dependency-caching#cache-access-for-low-trust-workflow-triggers).
+- GitHub Docs: [Controlling cache access with cache-mode](https://docs.github.com/actions/reference/workflows-and-actions/dependency-caching#controlling-cache-access-with-cache-mode).
 - Scribe Security Blog: [Cache Poisoning in GitHub Actions](https://scribesecurity.com/blog/github-cache-poisoning/).

actions/ql/src/Security/CWE-349/CachePoisoningViaPoisonableStep.md

@@ -1,6 +1,6 @@
 ## Overview
 
-GitHub Actions cache poisoning is a technique that allows an attacker to inject malicious content into the Action's cache from unprivileged workflow, potentially leading to code execution in privileged workflows.
+GitHub Actions cache poisoning is a technique that allows an attacker to inject malicious content into the Actions cache from an unprivileged workflow with cache-write access, potentially leading to code execution in privileged workflows.
 
 An attacker with the ability to run code in the context of the default branch (e.g. through Code Injection or Execution of Untrusted Code) can exploit this to:
 
@@ -23,7 +23,13 @@ Due to the above design, if something is cached in the context of the default br
 
 ## Recommendation
 
-1. Avoid using caching in workflows that handle sensitive operations like releases.
+Set `cache-mode: read` on workflows or jobs that process untrusted input and only need to restore
+caches, or `cache-mode: none` if they do not need cache access. These restrictions are enforced by
+the cache service. Job-level settings override workflow-level settings. Set an explicit mode on
+jobs that call reusable workflows to limit the access those workflows can request. Do not use
+`write-only` to prevent cache poisoning: it prevents restores but still permits saves.
+
+1. Avoid restoring caches in workflows that handle sensitive operations like releases. Use `cache-mode: none` to disable cache access.
 2. If caching must be used:
    - Validate restored cache contents before use.
    - Use short-lived, workflow-specific cache keys.
@@ -34,9 +40,13 @@ Due to the above design, if something is cached in the context of the default br
 
 ## Example
 
-GitHub gives workflows triggered by low-trust events, such as `issue_comment`,
+By default, GitHub gives workflows triggered by low-trust events, such as `issue_comment`,
 `pull_request_target`, and `workflow_run`, read-only access to the default branch cache scope.
-This query therefore reports only workflows whose trigger can write to that scope.
+An explicit `cache-mode: write` or `cache-mode: write-only` grants write access even for these
+triggers, while `read` and `none` prevent cache saves. Reusable workflows cannot exceed an explicit
+mode set by their caller, but can override an implicit trigger-based default.
+This query reports only jobs that can write to the default branch cache scope, accounting for
+the trigger, branch, and effective cache mode.
 
 ### Incorrect Usage
 
@@ -67,14 +77,16 @@ jobs:
 
 ### Correct Usage
 
-The following workflow runs untrusted code in a non-privileged job and the cache is scoped to the Pull Request branch.
+The following workflow runs untrusted code in a non-privileged job with the cache scoped to the
+pull request's merge ref. It also explicitly prevents cache saves with `cache-mode: read`.
 
 ```yaml
 name: Secure Workflow
 on:
   pull_request:
     branches: [main]
 permissions: {}
+cache-mode: read
 jobs:
   test:
     runs-on: ubuntu-latest
@@ -90,4 +102,5 @@ jobs:
 
 - Adnan Khan's Blog: [The Monsters in Your Build Cache – GitHub Actions Cache Poisoning](https://adnanthekhan.com/2024/05/06/the-monsters-in-your-build-cache-github-actions-cache-poisoning/).
 - GitHub Docs: [Cache access for low-trust workflow triggers](https://docs.github.com/actions/reference/workflows-and-actions/dependency-caching#cache-access-for-low-trust-workflow-triggers).
+- GitHub Docs: [Controlling cache access with cache-mode](https://docs.github.com/actions/reference/workflows-and-actions/dependency-caching#controlling-cache-access-with-cache-mode).
 - Scribe Security Blog: [Cache Poisoning in GitHub Actions](https://scribesecurity.com/blog/github-cache-poisoning/).

actions/ql/src/change-notes/2026-09-17-cache-mode.md

@@ -0,0 +1,5 @@
+---
+category: minorAnalysis
+---
+* The cache-poisoning queries now honor workflow and job `cache-mode` settings, including overrides and explicit limits in reusable-workflow call chains. Jobs with `read` or `none` access are excluded, while low-trust triggers that explicitly request `write` or `write-only` access can now be reported.
+* Cache-poisoning analysis now recognizes unfiltered pushes to the default branch and `pull_request` runs for merged `closed` events with write-capable cache modes.

actions/ql/test/query-tests/Security/CWE-349/.github/workflows/cache_mode_nested.yml

@@ -0,0 +1,34 @@
+on:
+  workflow_call:
+  workflow_dispatch:
+  push: # No cache alert: tag-only pushes cannot write the default-branch cache.
+    tags: ['v*']
+  pull_request: # No cache alert: closed PRs target a feature branch.
+    types: [closed]
+    branches: [feature]
+
+permissions: {}
+
+jobs:
+  inherited: # No cache alert: harmless inherited-mode probe.
+    runs-on: ubuntu-latest
+    steps:
+      - run: echo test
+
+  read: # No cache alert: read mode prevents saves and conflicts with write-only callers.
+    cache-mode: read
+    runs-on: ubuntu-latest
+    steps:
+      - run: echo test
+
+  write: # No cache alert: harmless probe; write exceeds a write-only caller's limit.
+    cache-mode: write
+    runs-on: ubuntu-latest
+    steps:
+      - run: echo test
+
+  write-only: # No cache alert: harmless probe of permitted cache saves.
+    cache-mode: write-only
+    runs-on: ubuntu-latest
+    steps:
+      - run: echo test