CVE-2015-2721

CVE-2015-2721 is a medium-severity vulnerability in Mozilla Network Security Services with a CVSS 2.0 base score of 4.3. 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-310.

Key facts

Description

Mozilla Network Security Services (NSS) before 3.19, as used in Mozilla Firefox before 39.0, Firefox ESR 31.x before 31.8 and 38.x before 38.1, Thunderbird before 38.1, and other products, does not properly determine state transitions for the TLS state machine, which allows man-in-the-middle attackers to defeat cryptographic protection mechanisms by blocking messages, as demonstrated by removing a forward-secrecy property by blocking a ServerKeyExchange message, aka a "SMACK SKIP-TLS" issue.

Frequently asked questions

What is CVE-2015-2721?
Mozilla Network Security Services (NSS) before 3.19, as used in Mozilla Firefox before 39.0, Firefox ESR 31.x before 31.8 and 38.x before 38.1, Thunderbird before 38.1, and other products, does not properly determine state transitions for the TLS state machine, which allows man-in-the-middle attackers to defeat cryptographic protection mechanisms by blocking messages, as demonstrated by removing a forward-secrecy property by blocking a ServerKeyExchange message, aka a "SMACK SKIP-TLS" issue.
How severe is CVE-2015-2721?
CVE-2015-2721 has a CVSS 2.0 base score of 4.3, rated medium severity.
Is CVE-2015-2721 being actively exploited?
It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 3% (87th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2015-2721?
CVE-2015-2721 primarily affects Mozilla Network Security Services. In total, 13 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.
How do I fix CVE-2015-2721?
Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.
When was CVE-2015-2721 published?
CVE-2015-2721 was published on 2015-07-06 and last updated on 2026-06-17.

References

Affected products (13)

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