CVE-2020-15272 (published 2020-10-26T19:15Z)

In the git-tag-annotation-action (open source GitHub Action) before version 1.0.1, an attacker can execute arbitrary (*) shell commands if they can control the value of [the `tag` input] or manage to alter the value of [the `GITHUB_REF` environment variable]. The problem has been patched in version 1.0.1. If you don't use the `tag` input you are most likely safe. The `GITHUB_REF` environment variable is protected by the GitHub Actions environment so attacks from there should be impossible. If you must use the `tag` input and cannot upgrade to `> 1.0.0` make sure that the value is not controlled by another Action.

Severity: MEDIUM
CVSS v2 base score: 6.5 (AV:N/AC:L/Au:S/C:P/I:P/A:P)
CVSS v3 base score: 9.6, CRITICAL (CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:N)

Weakness information:
cwe_id: CWE-78
cwe_name: Improper Neutralization of Special Elements used in an OS Command ('OS Command Injection')
description: The product constructs all or part of an OS command using externally-influenced input from an upstream component, but it does not neutralize or incorrectly neutralizes special elements that could modify the intended OS command when it is sent to a downstream component.
extended_description: 
		   This weakness can lead to a vulnerability in environments in which the attacker does not have direct access to the operating system, such as in web applications. Alternately, if the weakness occurs in a privileged program, it could allow the attacker to specify commands that normally would not be accessible, or to call alternate commands with privileges that the attacker does not have. The problem is exacerbated if the compromised process does not follow the principle of least privilege, because the attacker-controlled commands may run with special system privileges that increases the amount of damage.
            There are at least two subtypes of OS command injection:
               
				 The application intends to execute a single, fixed program that is under its own control. It intends to use externally-supplied inputs as arguments to that program. For example, the program might use system("nslookup [HOSTNAME]") to run nslookup and allow the user to supply a HOSTNAME, which is used as an argument. Attackers cannot prevent nslookup from executing. However, if the program does not remove command separators from the HOSTNAME argument, attackers could place the separators into the arguments, which allows them to execute their own program after nslookup has finished executing.
				 The application accepts an input that it uses to fully select which program to run, as well as which commands to use. The application simply redirects this entire command to the operating system. For example, the program might use "exec([COMMAND])" to execute the [COMMAND] that was supplied by the user. If the COMMAND is under attacker control, then the attacker can execute arbitrary commands or programs. If the command is being executed using functions like exec() and CreateProcess(), the attacker might not be able to combine multiple commands together in the same line.
               
            From a weakness standpoint, these variants represent distinct programmer errors. In the first variant, the programmer clearly intends that input from untrusted parties will be part of the arguments in the command to be executed. In the second variant, the programmer does not intend for the command to be accessible to any untrusted party, but the programmer probably has not accounted for alternate ways in which malicious attackers can provide input.
         
         

Fix information:
repo_url: https://github.com/ericcornelissen/git-tag-annotation-action
commit_details: repo_url: https://github.com/ericcornelissen/git-tag-annotation-action
author: Eric Cornelissen
author_date: 2020-10-24 21:29:06+03:00
msg: Fix shell injection bug

Fix a shell injection bug where an attacker controlling the "tag" value
in the code (i.e. the value of `process.env.GITHUB_REF` or of the
`with: tag` input value) can run arbitrary (*) shell commands.

Also, update the Action's branding, changing the Action icon from
"git-commit" to "tag".

(*): provided it is within the limits of the GitHub Actions environment
repository: repo_url: https://github.com/ericcornelissen/git-tag-annotation-action
repo_name: ericcornelissen/git-tag-annotation-action
description: GitHub Actions Action to get git tag annotations 
repo_language: Shell
owner: ericcornelissen
file_changes: filename: CHANGELOG.md
change_type: ModificationType.MODIFY
diff: @@ -9,6 +9,11 @@ Versioning].
 
 - _No changes yet_
 
+## [1.0.1] - 2020-10-24
+
+- Update Action icon.
+- Fix shell injection vulnerability.
+
 ## [1.0.0] - 2020-10-22
 
 - Run the Action to get the git tag annotation of the current tag.

programming_language: Markdown
filename: action.yml
change_type: ModificationType.MODIFY
diff: @@ -16,5 +16,5 @@ runs:
   main: 'lib/index.js'
 
 branding:
-  icon: 'git-commit'
+  icon: 'tag'
   color: 'gray-dark'

programming_language: CoffeeScript
filename: main.js
change_type: ModificationType.MODIFY
diff: @@ -1,6 +1,11 @@
 const core = require('@actions/core');
 const { exec } = require('child_process');
 
+// Based on https://stackoverflow.com/a/22827128
+function escapeShellArg(arg) {
+  return arg.replace(/'/g, `'\\''`);
+}
+
 function main() {
   try {
     let tag = process.env.GITHUB_REF;
@@ -8,13 +13,16 @@ function main() {
       tag = `refs/tags/${core.getInput('tag')}`;
     }
 
-    exec(`git for-each-ref --format='%(contents)' ${tag}`, (err, stdout) => {
-      if (err) {
-        core.setFailed(err);
-      } else {
-        core.setOutput('git-tag-annotation', stdout);
-      }
-    });
+    exec(
+      `git for-each-ref --format='%(contents)' '${escapeShellArg(tag)}'`,
+      (err, stdout) => {
+        if (err) {
+          core.setFailed(err);
+        } else {
+          core.setOutput('git-tag-annotation', stdout);
+        }
+      },
+    );
   } catch (error) {
     core.setFailed(error.message);
   }

programming_language: TypeScript
filename: main.test.js
change_type: ModificationType.MODIFY
diff: @@ -23,7 +23,7 @@ it.each([
   main();
 
   expect(child_process.exec).toHaveBeenCalledWith(
-    `git for-each-ref --format='%(contents)' refs/tags/${tag}`,
+    `git for-each-ref --format='%(contents)' 'refs/tags/${tag}'`,
     expect.any(Function),
   );
 });
@@ -46,7 +46,7 @@ it.each([
 
   expect(core.getInput).toHaveBeenCalledTimes(2);
   expect(child_process.exec).toHaveBeenCalledWith(
-    `git for-each-ref --format='%(contents)' refs/tags/${tag}`,
+    `git for-each-ref --format='%(contents)' 'refs/tags/${tag}'`,
     expect.any(Function),
   );
 });
@@ -89,3 +89,14 @@ it('sets an error if exec fails', () => {
   expect(core.setOutput).not.toHaveBeenCalled();
   expect(core.setFailed).toHaveBeenCalledTimes(1);
 });
+
+it('escapes malicious values from the input', () => {
+  core.getInput.mockReturnValue(`'; $(cat /etc/shadow)`);
+
+  main();
+
+  expect(child_process.exec).toHaveBeenCalledWith(
+    "git for-each-ref --format='%(contents)' 'refs/tags/'\\''; $(cat /etc/shadow)'",
+    expect.any(Function),
+  );
+});

programming_language: TypeScript