CVE-2023-39532

SES's dynamic import and spread operator provides possible path to arbitrary exfiltration and execution

Workarounds

On the web, providing a suitably constrained Content-Security-Policy mitigates most of the threat.

With XS, building a binary that lacks the ability to load modules at runtime mitigates the entirety of the threat. That will look like an implementation of fxFindModule in a file like xsPlatform.c that calls fxRejectModuleFile.

We highly advise applying the above patch for Node.js as there is no known work-around and Node.js’s module specifiers are exceedingly powerful, including support for data:text/javascript, style module specifier URLs.

References

No references at this time.

This is a hole in the confinement of guest applications under SES that may manifest as either the ability to exfiltrate information or execute arbitrary code depending on the configuration and implementation of the surrounding host.

Guest program running inside a Compartment with as few as no endowments can gain access to the surrounding host’s dynamic import by using dynamic import after the spread operator, like {...import(arbitraryModuleSpecifier)}.

On the web or in web extensions, a Content-Security-Policy following ordinary best practices likely mitigates both the risk of exfiltration and execution of arbitrary code, at least limiting the modules that the attacker can import to those that are already part of the application. However, without a Content-Security-Policy, dynamic import can be used to issue HTTP requests for either communication through the URL or for the execution of code reachable from that origin.

Within an XS worker, an attacker can use the host’s module system to the extent that the host has been configured. This typically only allows access to module code on the host’s file system and is of limited use to an attacker.

Within Node.js, the attacker gains access to Node.js’s module system. Importing the powerful builtins is not useful except insofar as there are side-effects and tempered because dynamic import returns a promise. Spreading a promise into an object renders the promises useless. However, Node.js allows importing data URLs, so this is a clear path to arbitrary execution.

The application does not adequately validate input before processing it, allowing unexpected values to reach sensitive code paths. Typical impact: varies by context: data corruption, logic bypass, or denial of service.

CVE-2023-39532 has a CVSS score of 9.8 (Critical). The vector is network-reachable, no privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (0.13.5, 0.14.5, 0.15.24, 0.16.1, 0.17.1, 0.18.7); upgrading removes the vulnerable code path.

Kodem intelligence

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All affected 0.* version trains have the following patch. Running npm update will obtain the patch on all affected projects using ^0.* style dependency constraints in their package.json.

From 33469e88bfb2bf34a161c265f10f808ce354a700 Mon Sep 17 00:00:00 2001
From: Kris Kowal <[email protected]>
Date: Thu, 27 Jul 2023 13:25:13 -0700
Subject: [PATCH] fix(fix): Censor spread import

---
 packages/ses/src/transforms.js       |  2 +-
 packages/ses/test/test-transforms.js | 22 +++++++++++++++++++++-
 2 files changed, 22 insertions(+), 2 deletions(-)

diff --git a/packages/ses/src/transforms.js b/packages/ses/src/transforms.js
index a0fc8d0ef..64a46cb53 100644
--- a/packages/ses/src/transforms.js
+++ b/packages/ses/src/transforms.js
@@ -106,7 +106,7 @@ export const evadeHtmlCommentTest = src => {
 // /////////////////////////////////////////////////////////////////////////////
 
 const importPattern = new FERAL_REG_EXP(
-  '(^|[^.])\\bimport(\\s*(?:\\(|/[/*]))',
+  '(^|[^.]|\\.\\.\\.)\\bimport(\\s*(?:\\(|/[/*]))',
   'g',
 );
 
diff --git a/packages/ses/test/test-transforms.js b/packages/ses/test/test-transforms.js
index cef0c02c1..8f6818b83 100644
--- a/packages/ses/test/test-transforms.js
+++ b/packages/ses/test/test-transforms.js
@@ -6,7 +6,7 @@ import {
 } from '../src/transforms.js';
 
 test('no-import-expression regexp', t => {
-  t.plan(9);
+  t.plan(13);
 
   // Note: we cannot define these as regular functions (and then stringify)
   // because the 'esm' module loader that we use for running the tests (i.e.
@@ -20,6 +20,7 @@ test('no-import-expression regexp', t => {
   const safe = 'const a = 1';
   const safe2 = "const a = notimport('evil')";
   const safe3 = "const a = importnot('evil')";
+  const safe4 = "const a = compartment.import('name')";
 
   const obvious = "const a = import('evil')";
   const whitespace = "const a = import ('evil')";
@@ -27,10 +28,14 @@ test('no-import-expression regexp', t => {
   const doubleSlashComment = "const a = import // hah\n('evil')";
   const newline = "const a = import\n('evil')";
   const multiline = "\nimport('a')\nimport('b')";
+  const spread = "{...import('exfil')}";
+  const spread2 = "{\n...\nimport\n('exfil')}";
+  const spread3 = "{\n...\nimport/**/\n('exfil')}";
 
   t.is(rejectImportExpressions(safe), safe, 'safe');
   t.is(rejectImportExpressions(safe2), safe2, 'safe2');
   t.is(rejectImportExpressions(safe3), safe3, 'safe3');
+  t.is(rejectImportExpressions(safe4), safe4, 'safe4');
   t.throws(
     () => rejectImportExpressions(obvious),
     { instanceOf: SyntaxError },
@@ -62,6 +67,21 @@ test('no-import-expression regexp', t => {
     'possible import expression rejected around line 2',
     'multiline',
   );
+  t.throws(
+    () => rejectImportExpressions(spread),
+    { instanceOf: SyntaxError },
+    'spread',
+  );
+  t.throws(
+    () => rejectImportExpressions(spread2),
+    { instanceOf: SyntaxError },
+    'spread2',
+  );
+  t.throws(
+    () => rejectImportExpressions(spread3),
+    { instanceOf: SyntaxError },
+    'spread3',
+  );
 });
 
 test('no-html-comment-expression regexp', t => {
-- 
2.40.1

1. What is CVE-2023-39532? CVE-2023-39532 is a critical-severity improper input validation vulnerability in ses (npm), affecting versions >= 0.13.0, < 0.13.5. It is fixed in 0.13.5, 0.14.5, 0.15.24, 0.16.1, 0.17.1, 0.18.7. The application does not adequately validate input before processing it, allowing unexpected values to reach sensitive code paths.
2. How severe is CVE-2023-39532? CVE-2023-39532 has a CVSS score of 9.8 (Critical). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
3. Which versions of ses are affected by CVE-2023-39532? ses (npm) versions >= 0.13.0, < 0.13.5 is affected.
4. Is there a fix for CVE-2023-39532? Yes. CVE-2023-39532 is fixed in 0.13.5, 0.14.5, 0.15.24, 0.16.1, 0.17.1, 0.18.7. Upgrade to this version or later.
5. Is CVE-2023-39532 exploitable, and should I be worried? Whether CVE-2023-39532 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
6. What actually determines whether CVE-2023-39532 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
7. How do I fix CVE-2023-39532?
   • Upgrade ses to 0.13.5 or later
   • Upgrade ses to 0.14.5 or later
   • Upgrade ses to 0.15.24 or later
   • Upgrade ses to 0.16.1 or later
   • Upgrade ses to 0.17.1 or later
   • Upgrade ses to 0.18.7 or later

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