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Vulnerability record · CVE-2013-0757 · published 13 January 2013

CVE-2013-0757: Firefox Chrome Object Wrapper prototype tampering allows chrome-privileged JS

Mozilla · Firefox

The Chrome Object Wrapper (COW) implementation in Mozilla Firefox, Thunderbird and SeaMonkey failed to block modification of an object's prototype, so a crafted HTML document can reference Object.prototype.__proto__ to break out of the wrapper. Because the escape yields chrome privileges, a web page can run arbitrary JavaScript with the browser's own privileges, which is a full compromise of the affected client.

9.3 CVSS 2.0 High EPSS 61% · top 0.9% CWE-20 · Improper input validation
9.3CVSS 2.0 base score
61%EPSS exploitation probability, 30 days
NoNot in CISA KEV
9Affected product versions listed by NVD
20References, 2 tagged exploit
16 Jun 2026Last modified by NVD

Description

The Chrome Object Wrapper (COW) implementation in Mozilla Firefox before 18.0, Firefox ESR 17.x before 17.0.2, Thunderbird before 17.0.2, Thunderbird ESR 17.x before 17.0.2, and SeaMonkey before 2.15 does not prevent modifications to the prototype of an object, which allows remote attackers to execute arbitrary JavaScript code with chrome privileges by referencing Object.prototype.__proto__ in a crafted HTML document.

AV:N/AC:M/Au:N/C:C/I:C/A:C

Automated analysis

Generated by VULONE's analysis model from the NVD record, CISA KEV and EPSS data on 19 September 2026. Confidence: high.

high priorityRemote code execution with chrome privileges and a high EPSS score, but exploitation requires the victim to load crafted content and the flaw is long fixed in current releases.

What it is

The Chrome Object Wrapper (COW) implementation in Mozilla Firefox, Thunderbird and SeaMonkey failed to block modification of an object's prototype, so a crafted HTML document can reference Object.prototype.__proto__ to break out of the wrapper. Because the escape yields chrome privileges, a web page can run arbitrary JavaScript with the browser's own privileges, which is a full compromise of the affected client.

Impact

An attacker who gets a victim to load a crafted page gains arbitrary JavaScript execution with chrome privileges, allowing code execution in the browser's trusted context and access to the user's data and system resources.

Attack surface

Reached over the network via a crafted HTML document rendered by the vulnerable browser or mail client; no authentication is required, but the victim must load the page or message, so some user interaction is needed.

Exploitation

Not listed in CISA KEV, but EPSS is 0.60859 (99.1st percentile) and the Mozilla Bugzilla reference is tagged Exploit, indicating public exploit material exists.

What to do

  • Upgrade Firefox to 18.0 or later, Firefox ESR to 17.0.2 or later, Thunderbird to 17.0.2 or later, and SeaMonkey to 2.15 or later.
  • Apply the vendor and distribution updates referenced in the Mozilla MFSA 2013-14 advisory and the openSUSE, SUSE and Ubuntu USNs.
  • If immediate upgrade is not possible, restrict browsing and mail rendering to trusted content and disable JavaScript where feasible.
  • Retire or isolate end-of-life browser and mail client versions that cannot receive this fix.

Detection

  • Hunt for Firefox, Thunderbird and SeaMonkey versions below 18.0, 17.0.2 and 2.15 respectively across endpoints.
  • Monitor proxy and IDS logs for pages or messages containing Object.prototype.__proto__ references delivered to vulnerable clients.
  • Review browser crash and exploit-protection telemetry for anomalous chrome-context script execution on affected hosts.

This assessment is produced automatically and is not human-reviewed. Verify against the vendor advisory before acting on it.

Affected products

9 vulnerable configurations from NVD's CPE data, grouped by vendor and product.

References

LinkTags
http://lists.opensuse.org/opensuse-security-announce/2013-01/msg00006.html Third Party Advisory
http://lists.opensuse.org/opensuse-security-announce/2013-01/msg00007.html Third Party Advisory
http://lists.opensuse.org/opensuse-security-announce/2013-01/msg00010.html Third Party Advisory
http://lists.opensuse.org/opensuse-security-announce/2013-01/msg00017.html Third Party Advisory
http://www.mozilla.org/security/announce/2013/mfsa2013-14.html Vendor Advisory
http://www.ubuntu.com/usn/USN-1681-1 Third Party Advisory
http://www.ubuntu.com/usn/USN-1681-2 Third Party Advisory
http://www.ubuntu.com/usn/USN-1681-4 Third Party Advisory
https://bugzilla.mozilla.org/show_bug.cgi?id=813901 ExploitIssue TrackingPatchVendor Advisory
https://oval.cisecurity.org/repository/search/definition/oval%3Aorg.mitre.oval%3Adef%3A16939 Third Party Advisory
http://lists.opensuse.org/opensuse-security-announce/2013-01/msg00006.html Third Party Advisory
http://lists.opensuse.org/opensuse-security-announce/2013-01/msg00007.html Third Party Advisory
http://lists.opensuse.org/opensuse-security-announce/2013-01/msg00010.html Third Party Advisory
http://lists.opensuse.org/opensuse-security-announce/2013-01/msg00017.html Third Party Advisory
http://www.mozilla.org/security/announce/2013/mfsa2013-14.html Vendor Advisory
http://www.ubuntu.com/usn/USN-1681-1 Third Party Advisory
http://www.ubuntu.com/usn/USN-1681-2 Third Party Advisory
http://www.ubuntu.com/usn/USN-1681-4 Third Party Advisory
https://bugzilla.mozilla.org/show_bug.cgi?id=813901 ExploitIssue TrackingPatchVendor Advisory
https://oval.cisecurity.org/repository/search/definition/oval%3Aorg.mitre.oval%3Adef%3A16939 Third Party Advisory

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Same products first, then exploited flaws of the same weakness class.

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Source: NIST National Vulnerability Database (record CVE-2013-0757), CISA KEV, FIRST EPSS (scores of 2026-09-27). This page is refreshed as NVD updates the record.