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Vulnerability record · CVE-2020-26950 · published 9 December 2020

CVE-2020-26950: Mozilla firefox use after free vulnerability

Mozilla · Firefox

In certain circumstances, the MCallGetProperty opcode can be emitted with unmet assumptions resulting in an exploitable use-after-free condition. This vulnerability affects Firefox < 82.0.3, Firefox ESR < 78.4.1, and Thunderbird < 78.4.2.

8.8 CVSS 3.1 High EPSS 42% · top 1.3% CWE-416 · Use after free
8.8CVSS 3.1 base score, v2 9.3
42%EPSS exploitation probability, 30 days
NoNot in CISA KEV
3Affected product versions listed by NVD
6References, 4 tagged exploit
17 Jun 2026Last modified by NVD

Description

In certain circumstances, the MCallGetProperty opcode can be emitted with unmet assumptions resulting in an exploitable use-after-free condition. This vulnerability affects Firefox < 82.0.3, Firefox ESR < 78.4.1, and Thunderbird < 78.4.2.

CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H

Affected products

3 vulnerable configurations from NVD's CPE data, grouped by vendor and product.

References

LinkTags
http://packetstormsecurity.com/files/166175/Firefox-MCallGetProperty-Write-Side-Effects-Use-After-Free.html ExploitThird Party AdvisoryVDB Entry
https://bugzilla.mozilla.org/show_bug.cgi?id=1675905 ExploitIssue TrackingVendor Advisory
https://www.mozilla.org/security/advisories/mfsa2020-49/ Vendor Advisory
http://packetstormsecurity.com/files/166175/Firefox-MCallGetProperty-Write-Side-Effects-Use-After-Free.html ExploitThird Party AdvisoryVDB Entry
https://bugzilla.mozilla.org/show_bug.cgi?id=1675905 ExploitIssue TrackingVendor Advisory
https://www.mozilla.org/security/advisories/mfsa2020-49/ Vendor Advisory

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Related vulnerabilities

Same products first, then exploited flaws of the same weakness class.

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Source: NIST National Vulnerability Database (record CVE-2020-26950), CISA KEV, FIRST EPSS (scores of 2026-09-26). This page is refreshed as NVD updates the record.