diff --git a/actions/setup/js/push_signed_commits.cjs b/actions/setup/js/push_signed_commits.cjs
index ce652f233be..802feddda69 100644
--- a/actions/setup/js/push_signed_commits.cjs
+++ b/actions/setup/js/push_signed_commits.cjs
@@ -1,10 +1,6 @@
 // @ts-check
 /// <reference types="@actions/github-script" />
 
-/** @type {typeof import("fs")} */
-const fs = require("fs");
-/** @type {typeof import("path")} */
-const path = require("path");
 const { ERR_API } = require("./error_codes.cjs");
 
 /**
@@ -80,6 +76,33 @@ function unquoteCPath(s) {
   return Buffer.from(bytes).toString("utf8");
 }
 
+/**
+ * Read a blob from a specific commit as a base64-encoded string using
+ * `git show <sha>:<path>`.  The raw bytes emitted by git are collected via
+ * the `exec.exec` stdout listener so that binary files are not corrupted by
+ * any UTF-8 decoding layer (unlike `exec.getExecOutput` which always passes
+ * stdout through a `StringDecoder('utf8')`).
+ *
+ * @param {string} sha - Commit SHA to read the blob from
+ * @param {string} filePath - Repo-relative path of the file
+ * @param {string} cwd - Working directory of the local git checkout
+ * @returns {Promise<string>} Base64-encoded file contents
+ */
+async function readBlobAsBase64(sha, filePath, cwd) {
+  /** @type {Buffer[]} */
+  const chunks = [];
+  await exec.exec("git", ["show", `${sha}:${filePath}`], {
+    cwd,
+    silent: true,
+    listeners: {
+      stdout: (/** @type {Buffer} */ data) => {
+        chunks.push(data);
+      },
+    },
+  });
+  return Buffer.concat(chunks).toString("base64");
+}
+
 /**
  * @fileoverview Signed Commit Push Helper
  *
@@ -180,8 +203,7 @@ async function pushSignedCommits({ githubClient, owner, repo, branch, baseRef, c
           if (dstMode === "100755") {
             core.warning(`pushSignedCommits: executable bit on ${renamedPath} will be lost in signed commit (GitHub GraphQL does not support mode 100755)`);
           }
-          const content = fs.readFileSync(path.join(cwd, renamedPath));
-          additions.push({ path: renamedPath, contents: content.toString("base64") });
+          additions.push({ path: renamedPath, contents: await readBlobAsBase64(sha, renamedPath, cwd) });
         } else if (status && status.startsWith("C")) {
           // Copy: source path is kept (no deletion), only the destination path is added
           const copiedPath = unquoteCPath(paths[1]);
@@ -196,8 +218,7 @@ async function pushSignedCommits({ githubClient, owner, repo, branch, baseRef, c
           if (dstMode === "100755") {
             core.warning(`pushSignedCommits: executable bit on ${copiedPath} will be lost in signed commit (GitHub GraphQL does not support mode 100755)`);
           }
-          const content = fs.readFileSync(path.join(cwd, copiedPath));
-          additions.push({ path: copiedPath, contents: content.toString("base64") });
+          additions.push({ path: copiedPath, contents: await readBlobAsBase64(sha, copiedPath, cwd) });
         } else {
           // Added or Modified
           if (dstMode === "120000") {
@@ -207,8 +228,7 @@ async function pushSignedCommits({ githubClient, owner, repo, branch, baseRef, c
           if (dstMode === "100755") {
             core.warning(`pushSignedCommits: executable bit on ${filePath} will be lost in signed commit (GitHub GraphQL does not support mode 100755)`);
           }
-          const content = fs.readFileSync(path.join(cwd, filePath));
-          additions.push({ path: filePath, contents: content.toString("base64") });
+          additions.push({ path: filePath, contents: await readBlobAsBase64(sha, filePath, cwd) });
         }
       }
 
diff --git a/actions/setup/js/push_signed_commits.test.cjs b/actions/setup/js/push_signed_commits.test.cjs
index d3c9e6f5084..bcc3f5caf18 100644
--- a/actions/setup/js/push_signed_commits.test.cjs
+++ b/actions/setup/js/push_signed_commits.test.cjs
@@ -186,17 +186,24 @@ function makeRealExec(cwd) {
     /**
      * @param {string} program
      * @param {string[]} args
-     * @param {{ cwd?: string, env?: NodeJS.ProcessEnv }} [opts]
+     * @param {{ cwd?: string, env?: NodeJS.ProcessEnv, silent?: boolean, listeners?: { stdout?: (data: Buffer) => void } }} [opts]
      */
     exec: async (program, args, opts = {}) => {
+      const stdoutListener = opts.listeners?.stdout;
       const result = spawnSync(program, args, {
-        encoding: "utf8",
+        // Use raw Buffer encoding when a stdout listener is provided so binary
+        // content is not corrupted by UTF-8 decoding.
+        encoding: stdoutListener ? null : "utf8",
         cwd: opts.cwd ?? cwd,
         env: opts.env ?? { ...process.env, GIT_CONFIG_NOSYSTEM: "1", HOME: os.tmpdir() },
       });
       if (result.error) throw result.error;
       if (result.status !== 0) {
-        throw new Error(`${program} ${args.join(" ")} failed:\n${result.stderr}`);
+        const stderr = Buffer.isBuffer(result.stderr) ? result.stderr.toString("utf8") : (result.stderr ?? "");
+        throw new Error(`${program} ${args.join(" ")} failed:\n${stderr}`);
+      }
+      if (stdoutListener && result.stdout) {
+        stdoutListener(Buffer.isBuffer(result.stdout) ? result.stdout : Buffer.from(result.stdout));
       }
       return result.status ?? 0;
     },
@@ -324,6 +331,47 @@ describe("push_signed_commits integration tests", () => {
       expect(headlines).toEqual(["Add file-a.txt", "Add file-b.txt"]);
     });
 
+    it("each commit in a series should carry its own file content, not the working-tree tip", async () => {
+      // Regression test for the bug where fs.readFileSync always read from the
+      // working tree (HEAD), so intermediate commits A and B would contain the
+      // content of C when A→B→C were replayed.
+      execGit(["checkout", "-b", "versioned-branch"], { cwd: workDir });
+
+      fs.writeFileSync(path.join(workDir, "data.txt"), "version A\n");
+      execGit(["add", "data.txt"], { cwd: workDir });
+      execGit(["commit", "-m", "Version A"], { cwd: workDir });
+
+      fs.writeFileSync(path.join(workDir, "data.txt"), "version B\n");
+      execGit(["add", "data.txt"], { cwd: workDir });
+      execGit(["commit", "-m", "Version B"], { cwd: workDir });
+
+      fs.writeFileSync(path.join(workDir, "data.txt"), "version C\n");
+      execGit(["add", "data.txt"], { cwd: workDir });
+      execGit(["commit", "-m", "Version C"], { cwd: workDir });
+
+      execGit(["push", "-u", "origin", "versioned-branch"], { cwd: workDir });
+
+      global.exec = makeRealExec(workDir);
+      const githubClient = makeMockGithubClient();
+
+      await pushSignedCommits({
+        githubClient,
+        owner: "test-owner",
+        repo: "test-repo",
+        branch: "versioned-branch",
+        baseRef: "origin/main",
+        cwd: workDir,
+      });
+
+      expect(githubClient.graphql).toHaveBeenCalledTimes(3);
+      const calls = githubClient.graphql.mock.calls.map(c => c[1].input);
+
+      // Each commit must carry its own version of data.txt, not the working-tree tip (C)
+      expect(Buffer.from(calls[0].fileChanges.additions[0].contents, "base64").toString()).toBe("version A\n");
+      expect(Buffer.from(calls[1].fileChanges.additions[0].contents, "base64").toString()).toBe("version B\n");
+      expect(Buffer.from(calls[2].fileChanges.additions[0].contents, "base64").toString()).toBe("version C\n");
+    });
+
     it("should include deletions when files are removed in a commit", async () => {
       execGit(["checkout", "-b", "delete-branch"], { cwd: workDir });