CVE-2021-23953
If a user clicked into a specifically crafted PDF, the PDF reader could be confused into leaking cross-origin information, when said information is served as chunked data.
Does this matter?
Lower severity and a low EPSS score (1.06%). Track it; it rarely justifies an emergency change on its own.
Description
If a user clicked into a specifically crafted PDF, the PDF reader could be confused into leaking cross-origin information, when said information is served as chunked data. This vulnerability affects Firefox < 85, Thunderbird < 78.7, and Firefox ESR < 78.7.
- CVSS 3.1
- 4.3 MEDIUMCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:N/A:N
- EPSS
- 1.06% probability · 64th percentile
- Public exploits
- None in Exploit-DB
- CISA KEV
- Not listed
- Affected
- mozilla/firefox · mozilla/firefox esr · mozilla/thunderbird
- Source
- security@mozilla.org
EPSS 1.1% since 26 October 2026; no change recorded yet. Points are recorded when the score first appears and whenever it moves by a percentage point or more.
References
- https://bugzilla.mozilla.org/show_bug.cgi?id=1683940Issue Tracking, Permissions Required, Vendor Advisory
- https://www.mozilla.org/security/advisories/mfsa2021-03/Release Notes, Vendor Advisory
- https://www.mozilla.org/security/advisories/mfsa2021-04/Release Notes, Vendor Advisory
- https://www.mozilla.org/security/advisories/mfsa2021-05/Release Notes, Vendor Advisory
- https://bugzilla.mozilla.org/show_bug.cgi?id=1683940Issue Tracking, Permissions Required, Vendor Advisory
- https://www.mozilla.org/security/advisories/mfsa2021-03/Release Notes, Vendor Advisory
- https://www.mozilla.org/security/advisories/mfsa2021-04/Release Notes, Vendor Advisory
- https://www.mozilla.org/security/advisories/mfsa2021-05/Release Notes, Vendor Advisory
Source: NVD record, EPSS from FIRST.org, KEV from CISA, exploits from Exploit-DB. Refreshed daily. Download this record as JSON.