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

Critical severity GitHub Reviewed Published Aug 7, 2023 in endojs/endo • Updated Nov 11, 2023

Package

npm ses (npm)

Affected versions

>= 0.13.0, < 0.13.5
>= 0.14.0, < 0.14.5
>= 0.15.0, < 0.15.24
= 0.16.0
= 0.17.0
>= 0.18.0, < 0.18.7

Patched versions

0.13.5
0.14.5
0.15.24
0.16.1
0.17.1
0.18.7

Description

Impact

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.

Patches

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 <kris@agoric.com>
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

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.

References

@kriskowal kriskowal published to endojs/endo Aug 7, 2023
Published by the National Vulnerability Database Aug 8, 2023
Published to the GitHub Advisory Database Aug 9, 2023
Reviewed Aug 9, 2023
Last updated Nov 11, 2023

Severity

Critical

CVSS overall score

This score calculates overall vulnerability severity from 0 to 10 and is based on the Common Vulnerability Scoring System (CVSS).
/ 10

CVSS v3 base metrics

Attack vector
Network
Attack complexity
Low
Privileges required
None
User interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High

CVSS v3 base metrics

Attack vector: More severe the more the remote (logically and physically) an attacker can be in order to exploit the vulnerability.
Attack complexity: More severe for the least complex attacks.
Privileges required: More severe if no privileges are required.
User interaction: More severe when no user interaction is required.
Scope: More severe when a scope change occurs, e.g. one vulnerable component impacts resources in components beyond its security scope.
Confidentiality: More severe when loss of data confidentiality is highest, measuring the level of data access available to an unauthorized user.
Integrity: More severe when loss of data integrity is the highest, measuring the consequence of data modification possible by an unauthorized user.
Availability: More severe when the loss of impacted component availability is highest.
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

EPSS score

0.286%
(69th percentile)

Weaknesses

CVE ID

CVE-2023-39532

GHSA ID

GHSA-9c4h-3f7h-322r

Source code

Credits

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