diff --git a/.github/workflows/contributor-rewards.yml b/.github/workflows/contributor-rewards.yml
index 88ee1cf1c..e2a6a9311 100644
--- a/.github/workflows/contributor-rewards.yml
+++ b/.github/workflows/contributor-rewards.yml
@@ -1,4 +1,21 @@
 ---
+# Security note: this workflow intentionally uses `pull_request_target` so the
+# `reward user` label can fire on PRs from forks (the plain `pull_request`
+# trigger cannot see labels applied to fork PRs and runs under a read-only
+# GITHUB_TOKEN that cannot post comments / add labels).
+#
+# The job is bounded:
+#   - it never checks out fork code (no `actions/checkout` with `pull_request.head.ref`)
+#   - it never executes arbitrary scripts from the PR
+#   - the only side effects are: posting a templated comment and adding a label
+#   - permissions are minimal (contents:read, issues:write, pull-requests:read)
+#   - all PR/issue user metadata interpolated into search queries or comment
+#     bodies is treated as untrusted and normalized through safeLogin/safeUrl
+#     before use (see the inline script below).
+#
+# Do NOT broaden permissions, add a fork checkout, or remove the input
+# normalization without a security review.
+
 name: Contributor Rewards
 
 on:
@@ -47,6 +64,25 @@ jobs:
             const merchUrl = (process.env.CONTRIBUTOR_REWARD_MERCH_URL || '').trim();
             const customMessage = (process.env.CONTRIBUTOR_REWARD_MESSAGE || '').trim();
 
+            // Treat all PR/issue metadata as untrusted display-only data — this
+            // workflow runs under `pull_request_target` so anything coming from
+            // a fork (login, html_url) crosses a trust boundary. Normalize
+            // before interpolating into search queries or comment bodies.
+            // GitHub usernames are 1-39 chars, alphanumeric + hyphen.
+            const safeLogin = (s) => String(s || '').replace(/[^A-Za-z0-9-]/g, '').slice(0, 39);
+            // Only allow github.com / *.github.com (covers GitHub Enterprise).
+            // Strip query/fragment to defeat comment-body injection via crafted
+            // URLs. Return '' if the URL is unparseable or off-host.
+            const safeUrl = (s) => {
+              try {
+                const u = new URL(String(s || ''));
+                const okHost = u.hostname === 'github.com' || u.hostname.endsWith('.github.com');
+                return okHost ? `${u.origin}${u.pathname}` : '';
+              } catch {
+                return '';
+              }
+            };
+
             const normalize = value => String(value || '').trim().toLowerCase();
             const triggerLabelKey = normalize(triggerLabel);
 
@@ -94,12 +130,19 @@ jobs:
                     return null;
                   }
 
+                  const login = safeLogin(pr.user?.login);
+                  if (!login) {
+                    core.info(`PR #${pr.number} has an unrecognized author login shape; skipping.`);
+                    return null;
+                  }
+                  const htmlUrl = safeUrl(pr.html_url);
+
                   return {
                     kind: 'pull request',
                     number: pr.number,
-                    htmlUrl: pr.html_url,
-                    login: pr.user.login,
-                    userType: pr.user.type,
+                    htmlUrl,
+                    login,
+                    userType: pr.user?.type,
                     reason: 'first merged pull request',
                     manualOverride: false,
                     requireFirstMergedPr: true,
@@ -112,12 +155,19 @@ jobs:
                     return null;
                   }
 
+                  const login = safeLogin(pr.user?.login);
+                  if (!login) {
+                    core.info(`PR #${pr.number} has an unrecognized author login shape; skipping.`);
+                    return null;
+                  }
+                  const htmlUrl = safeUrl(pr.html_url);
+
                   return {
                     kind: 'pull request',
                     number: pr.number,
-                    htmlUrl: pr.html_url,
-                    login: pr.user.login,
-                    userType: pr.user.type,
+                    htmlUrl,
+                    login,
+                    userType: pr.user?.type,
                     reason: `maintainer-applied "${triggerLabel}" label on a pull request`,
                     manualOverride: true,
                     requireFirstMergedPr: false,
@@ -139,12 +189,19 @@ jobs:
                   return null;
                 }
 
+                const login = safeLogin(issue.user?.login);
+                if (!login) {
+                  core.info(`Issue #${issue.number} has an unrecognized author login shape; skipping.`);
+                  return null;
+                }
+                const htmlUrl = safeUrl(issue.html_url);
+
                 return {
                   kind: 'issue',
                   number: issue.number,
-                  htmlUrl: issue.html_url,
-                  login: issue.user.login,
-                  userType: issue.user.type,
+                  htmlUrl,
+                  login,
+                  userType: issue.user?.type,
                   reason: `maintainer-applied "${triggerLabel}" label on an issue`,
                   manualOverride: true,
                   requireFirstMergedPr: false,