CVE-2022-31736 — A malicious website could have learned the size of a cross-origin resource that

A malicious website could have learned the size of a cross-origin resource that supported Range requests. This vulnerability affects Thunderbird < 91.10, Firefox < 101, and Firefox ESR < 91.10.

01What is this vulnerability?

A malicious website could have learned the size of a cross-origin resource that supported Range requests. This vulnerability affects Thunderbird < 91.10, Firefox < 101, and Firefox ESR < 91.10.

02Affected products

Vendor	Product	Versions
Mozilla	Thunderbird	unspecified
Mozilla	Firefox	unspecified
Mozilla	Firefox ESR	unspecified

03Active exploitation status

Not currently listed on the CISA Known Exploited Vulnerabilities (KEV) catalog. EPSS is the best forward-looking signal — see the EPSS row above.

04Recommended remediation

• Patch to a fixed version listed in the vendor advisory (see references below).
• Mitigate with WAF rules, network egress filters, or feature flags where the patch is not yet available.
• Hunt historical logs for exploitation indicators — see Detection signatures below.

05Technical details

For the full vendor write-up, exploit chains, and reference implementations, see the references list in section 09.

06Detection signatures

Ask SARA in chat to draft a starting detection for this CVE in your stack of choice.

07Related CVEs

No directly-cited follow-up CVEs in the KB record for this advisory. The references list in section 09 carries the vendor cross-references.

08Timeline

• Published: 2022-12-22T00:00:00.000Z
• Last modified: 2025-04-15T14:58:07.022Z

09References

• www.mozilla.org — https://www.mozilla.org/security/advisories/mfsa2022-20/
• www.mozilla.org — https://www.mozilla.org/security/advisories/mfsa2022-22/
• www.mozilla.org — https://www.mozilla.org/security/advisories/mfsa2022-21/
• bugzilla.mozilla.org — https://bugzilla.mozilla.org/show_bug.cgi?id=1735923