CVE-2009-2477

CVE-2009-2477 is a critical-severity vulnerability in Mozilla Firefox with a CVSS 2.0 base score of 9.3. Its EPSS exploit-prediction score of 43% places it in the 99th percentile, indicating an elevated likelihood of exploitation. The underlying weakness is classified as CWE-94.

Key facts

• Severity: Critical (CVSS 2.0 base score 9.3)
• EPSS exploit prediction: 43% (99th percentile)
• Actively exploited: Not listed in CISA KEV
• Weakness: CWE-94
• Affected product: Mozilla Firefox
• Published: 2009-07-15
• Last modified: 2026-06-16

Description

js/src/jstracer.cpp in the Just-in-time (JIT) JavaScript compiler (aka TraceMonkey) in Mozilla Firefox 3.5 before 3.5.1 allows remote attackers to execute arbitrary code via certain use of the escape function that triggers access to uninitialized memory locations, as originally demonstrated by a document containing P and FONT elements.

Frequently asked questions

What is CVE-2009-2477?

js/src/jstracer.cpp in the Just-in-time (JIT) JavaScript compiler (aka TraceMonkey) in Mozilla Firefox 3.5 before 3.5.1 allows remote attackers to execute arbitrary code via certain use of the escape function that triggers access to uninitialized memory locations, as originally demonstrated by a document containing P and FONT elements.

How severe is CVE-2009-2477?

CVE-2009-2477 has a CVSS 2.0 base score of 9.3, rated critical severity.

Is CVE-2009-2477 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 43% (99th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2009-2477?

CVE-2009-2477 affects Mozilla Firefox. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2009-2477?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its critical severity, prioritise patching exposed systems.

When was CVE-2009-2477 published?

CVE-2009-2477 was published on 2009-07-15 and last updated on 2026-06-16.

References

• http://blog.mozilla.com/security/2009/07/14/critical-javascript-vulnerability-in-firefox-35/
• http://isc.sans.org/diary.html?storyid=6796
• http://secunia.com/advisories/35798
• http://sunsolve.sun.com/search/document.do?assetkey=1-66-266148-1
• http://voices.washingtonpost.com/securityfix/2009/07/stopgap_fix_for_critical_firef.html
• http://www.exploit-db.com/exploits/9137
• http://www.exploit-db.com/exploits/9181
• http://www.h-online.com/security/First-Zero-Day-Exploit-for-Firefox-3-5--/news/113761
• http://www.kb.cert.org/vuls/id/443060
• http://www.mozilla.org/security/announce/2009/mfsa2009-41.html
• http://www.securityfocus.com/bid/35660
• http://www.vupen.com/english/advisories/2009/1868
• https://bugzilla.mozilla.org/show_bug.cgi?id=503286
• https://www.exploit-db.com/exploits/40936/
• https://www.redhat.com/archives/fedora-package-announce/2009-July/msg00909.html

Affected products (1)

• cpe:2.3:a:mozilla:firefox:3.5:*:*:*:*:*:*:*

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