CVE-2015-2721
MEDIUMEPSS 87th pctlDescription
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 to fix
Remediation is compiled from vendor and distribution security advisories. Always confirm against the linked source for your exact version and platform.
CVSS v2 Vector
No CVSS vector data available.
Exploit Intelligence
Elevated risk: more likely to be exploited than 87% of all known CVEs.
References
Related Vulnerabilities
Other CWE-310 (Cryptographic Issues) vulnerabilities, ordered by exploit likelihood. View all
| CVE | Severity | CVSS | EPSS | Exploited | Fix |
|---|---|---|---|---|---|
| CVE-2014-3566 | Low | 3.4 | 100% | - | Fix |
| CVE-2015-4000 | Low | 3.7 | 100% | - | Fix |
| CVE-2015-0204 | Medium | 4.3 | 99% | - | Fix |
| CVE-2016-2107 | Medium | 5.9 | 89% | - | Fix |
| CVE-2016-0800 | Medium | 5.9 | 82% | - | Fix |
| CVE-2014-8684 | Critical | 9.8 | 72% | - | - |
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Markdown
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Start freeThis product uses NVD data but is not endorsed or certified by the NVD. EPSS scores courtesy of FIRST.org (https://www.first.org/epss). Source: CISA KEV Catalog. Data as of 2026-05-06.