CVE-2015-4520

CVE-2015-4520 is a medium-severity vulnerability in Mozilla Firefox with a CVSS 2.0 base score of 6.4. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-254.

Key facts

Description

Mozilla Firefox before 41.0 and Firefox ESR 38.x before 38.3 allow remote attackers to bypass CORS preflight protection mechanisms by leveraging (1) duplicate cache-key generation or (2) retrieval of a value from an incorrect HTTP Access-Control-* response header.

Frequently asked questions

What is CVE-2015-4520?
Mozilla Firefox before 41.0 and Firefox ESR 38.x before 38.3 allow remote attackers to bypass CORS preflight protection mechanisms by leveraging (1) duplicate cache-key generation or (2) retrieval of a value from an incorrect HTTP Access-Control-* response header.
How severe is CVE-2015-4520?
CVE-2015-4520 has a CVSS 2.0 base score of 6.4, rated medium severity.
Is CVE-2015-4520 being actively exploited?
It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 3% (86th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2015-4520?
CVE-2015-4520 primarily affects Mozilla Firefox. In total, 8 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.
How do I fix CVE-2015-4520?
Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.
When was CVE-2015-4520 published?
CVE-2015-4520 was published on 2015-09-24 and last updated on 2026-06-17.

References

Affected products (8)

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