What is CVE-2024-7531?

CVE-2024-7531 is a medium-severity vulnerability in Mozilla Firefox, classified under Time-of-check Time-of-use (TOCTOU) Race Condition. CVSS score: 6.5/10. Published 2024-08-06.

How severe is CVE-2024-7531?

Medium severity. CVSS v3 base score is 6.5 out of 10.

Is CVE-2024-7531 known to be exploited?

1 public proof-of-concept repositories are indexed. Not currently listed in the CISA KEV catalog.

Vulnerability in Mozilla Firefox

CVE-2024-7531

Calling `PK11_Encrypt()` in NSS using CKM_CHACHA20 and the same buffer for input and output can result in plaintext on an Intel Sandy Bridge processor. In Firefox this only affects the QUIC header protection feature when the connection is using the ChaCha20-Poly1305 cipher suite. The most likely outcome is connection failure, but if the connection persists despite the high packet loss it could be possible for a network observer to identify packets as coming from the same source despite a network path change. This vulnerability affects Firefox < 129, Firefox ESR < 115.14, and Firefox ESR < 128.1.

Vulnerability class: TOCTOU (Time-of-Check to Time-of-Use)

Published 2024-08-06 · last modified 2026-06-17.

CVSS v3 metric

CVSS v3 base score 6.5 (Medium). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:N/A:N.

EPSS exploit prediction

EPSS: 0.004 (35.7th percentile), scored 2026-10-01.

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 36th percentile — 35.7% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.004 · newest: 0.004 · change: 0.000

Affected products

Mozilla Firefox — versions unspecified
Mozilla Firefox Esr — versions unspecified
Mozilla Firefox Esr — versions 128.0

Weakness classification (CWE)

CWE-367 — Time-of-check Time-of-use (TOCTOU) Race Condition

Public proof-of-concept exploits

fkie-cad/nvd-json-data-feeds

References

bugzilla.mozilla.org/show_bug.cgi (Permissions Required, Issue Tracking)
www.mozilla.org/security/advisories/mfsa2024-33/ (Vendor Advisory)
www.mozilla.org/security/advisories/mfsa2024-34/ (Vendor Advisory)
www.mozilla.org/security/advisories/mfsa2024-35/ (Vendor Advisory)

Frequently asked questions

What is CVE-2024-7531?: CVE-2024-7531 is a medium-severity vulnerability in Mozilla Firefox, classified under Time-of-check Time-of-use (TOCTOU) Race Condition. CVSS score: 6.5/10. Published 2024-08-06.
How severe is CVE-2024-7531?: Medium severity. CVSS v3 base score is 6.5 out of 10.
Is CVE-2024-7531 known to be exploited?: 1 public proof-of-concept repositories are indexed. Not currently listed in the CISA KEV catalog.