CVE-2020-26950

Exp

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.

Published: 2020-12-09 Last update: 2026-06-17 Assigner: [email protected] Source: [email protected]
NVD Status：Modified，CVE State: published
View at NVD, CVE.org, EUVD

CVE-2020-26950 is rated High Exploit Risk (79.7/100): CVSS High severity, with high exploitation likelihood (EPSS 42.60%, 99th percentile). 2 public exploit reference(s) are indexed (Exploit-DB). Public exploits are available—assess exposure, apply mitigations, and prioritize patching.

Risk is dynamic; we continuously reassess and refresh what is shown on this page as upstream context changes.

Public exploit references (Exploit-DB) for CVE-2020-26950

EDB-ID Source Kind Published Link
— nvd_ref exploit_tag Exploit-DB ↗
— nvd_ref exploit_tag Exploit-DB ↗

Exploit prediction scoring system (EPSS) score for CVE-2020-26950

EPSS lead: Daily EPSS estimates relative likelihood of exploitation; percentile ranks this CVE among scored vulnerabilities (higher = more severe relative rank).

# Date Old EPSS score New EPSS score Delta (New - Old)
1 2026-06-15 48.27% 42.60% -5.68%
2 2026-03-31 46.89% 48.27% +1.38%
3 2026-02-25 — 46.89% —

Full EPSS history (45 records total)

Common vulnerability scoring system (CVSS) metrics for CVE-2020-26950

CVSS metrics for this CVE.

Base score Version Severity Vector Exploitability Impact Score source
8.8 3.1 HIGH
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H Click to expand
Attack vector (AV:N)
Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
Attack complexity (AC:L)
Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
Privileges required (PR:N)
No account or special rights needed—anonymous or random user is enough.
User interaction (UI:R)
A real person has to do something—click, install, enable—otherwise it doesn’t land.
Scope (S:U)
Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:H)
Serious risk that confidential data gets exposed in a big way.
Integrity (I:H)
They could widely tamper with or forge data—trust in the data is badly hurt.
Availability (A:H)
Could take the service down hard or make it unusable for people who depend on it.
 2.8 5.9 [email protected]
9.3 2.0 HIGH
AV:N/AC:M/Au:N/C:C/I:C/A:C Click to expand
Access vector (AV:N)
Can be exploited remotely over network reachability.
Access complexity (AC:M)
Exploitation needs some favorable conditions, but not exceptional ones.
Authentication (AU:N)
No authentication is required.
Confidentiality impact (C:C)
Complete confidentiality impact.
Integrity impact (I:C)
Complete integrity impact.
Availability impact (A:C)
Complete availability impact.
 8.6 10.0 [email protected]

Weakness enumeration for CVE-2020-26950

OS Trackers for CVE-2020-26950

vendor priority summary link
alpine high CVE-2020-26950: 5 source package rows (firefox, firefox-esr, librewolf, mozjs78, thunderbird); 63 state rows across 7 repos (3.17-community, 3.18-community, 3.19-community, 3.20-community, 3.21-community, 3.22-community, edge-community); fixed 33, open 30. https://security.alpinelinux.org/vuln/CVE-2020-26950
debian not yet assigned CVE-2020-26950 not yet assigned priority: Debian including 3 source packages (firefox, firefox-esr, thunderbird), 11 status rows across 5 suites (bookworm, bullseye, forky, sid, trixie): resolved 11. https://security-tracker.debian.org/tracker/CVE-2020-26950
gentoo normal CVE-2020-26950: 1 GLSA(s) (202011-07), 2 atom(s) (www-client/firefox, www-client/firefox-bin); latest impact normal. https://bugs.gentoo.org/buglist.cgi?quicksearch=CVE-2020-26950
redhat critical — https://access.redhat.com/security/cve/CVE-2020-26950
suse high CVE-2020-26950 severity important: SUSE including 76 source package names (MozillaFirefox-140.2.0-160000.1.2, MozillaFirefox-78.10.0-8.38.1, …), 206 product×package rows across 69 product lines (Container suse/kiosk/firefox-esr, HPE Helion OpenStack 8, … (69 product lines)): Fixed 200, Known Not Affected 6. https://www.suse.com/security/cve/CVE-2020-26950/
ubuntu high CVE-2020-26950 high priority: Ubuntu including 6 source packages (firefox, mozjs38, mozjs52, mozjs60, mozjs68, thunderbird), 78 status rows across 13 suites (bionic, focal, groovy, hirsute, impish, jammy, kinetic, lunar, mantic, noble, trusty, upstream, xenial): DNE 44, released 23, ignored 11. https://ubuntu.com/security/CVE-2020-26950

Affected software / configurations for CVE-2020-26950

Vendor Product Version Raw CPE
mozilla firefox < 82.0.3 cpe:2.3:a:mozilla:firefox:*:*:*:*:*:*:*:*
mozilla firefox_esr < 78.4.1 cpe:2.3:a:mozilla:firefox_esr:*:*:*:*:*:*:*:*
mozilla thunderbird < 78.4.2 cpe:2.3:a:mozilla:thunderbird:*:*:*:*:*:*:*:*

References for CVE-2020-26950

cvelogic Threat Intelligence