CVE-2026-8391 | Other issue in the JavaScript Engine component

Other issue in the JavaScript Engine component. This vulnerability was fixed in Firefox 150.0.3, Firefox ESR 115.36, Firefox ESR 140.11, and Thunderbird 140.11.

Published: 2026-05-12 Last update: 2026-06-29 Assigner: [email protected] Source: [email protected]
NVD Status：Modified，CVE State: published
View at NVD, CVE.org, EUVD

CVE-2026-8391 is rated Low Risk (28.8/100): CVSS Medium severity, with low exploitation likelihood (EPSS 0.30%). Monitor for updates and reassess as exploit intelligence or EPSS changes.

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

Exploit prediction scoring system (EPSS) score for CVE-2026-8391

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 2026-06-30 0.21% 0.30% +0.08%
2 2026-06-15 0.06% 0.21% +0.16%
3 2026-05-14 — 0.06% —

Full EPSS history (4 records total)

Common vulnerability scoring system (CVSS) metrics for CVE-2026-8391

CVSS metrics for this CVE.

Base score Version Severity Vector Exploitability Impact Score source
5.3 3.1 MEDIUM
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N 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:N)
Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:U)
Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:L)
Some sensitive info could get out, but not a total data dump.
Integrity (I:N)
Data isn’t meaningfully altered or forged.
Availability (A:N)
Service keeps running; no real outage angle.
 3.9 1.4 134c704f-9b21-4f2e-91b3-4a467353bcc0
7.5 3.1 HIGH
CVSS:3.1/AV:N/AC:H/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:H)
Even with access, the exploit needs extra luck, timing, or a fussy environment to actually work.
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.
 1.6 5.9 0b0ca135-0b70-47e7-9f44-1890c2a1c46c

Weakness enumeration for CVE-2026-8391

GitHub Security Advisory for CVE-2026-8391

GHSA-93pv-vhrf-wv64 · Severity: medium — Other issue in the JavaScript Engine component. This vulnerability was fixed in Firefox 150.0.3.

OS Trackers for CVE-2026-8391

vendor priority summary link
debian not yet assigned CVE-2026-8391 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-2026-8391
ubuntu medium CVE-2026-8391 medium priority: Ubuntu including 9 source packages (firefox, mozjs102, …), 49 status rows across 7 suites (bionic, focal, jammy, noble, questing, resolute, upstream): DNE 23, needs-triage 10, ignored 8, not-affected 7, needed 1. https://ubuntu.com/security/CVE-2026-8391

Affected software / configurations for CVE-2026-8391

Vendor Product Version Raw CPE
mozilla firefox < 150.0.3 cpe:2.3:a:mozilla:firefox:*:*:*:*:-:*:*:*

References for CVE-2026-8391

URL Tags
https://bugzilla.mozilla.org/show_bug.cgi?id=2038575 Permissions Required
https://www.mozilla.org/security/advisories/mfsa2026-45/ Vendor Advisory
https://www.mozilla.org/security/advisories/mfsa2026-47/
https://www.mozilla.org/security/advisories/mfsa2026-48/
https://www.mozilla.org/security/advisories/mfsa2026-51/
https://access.redhat.com/errata/RHSA-2026:21378
https://access.redhat.com/errata/RHSA-2026:21380
https://access.redhat.com/errata/RHSA-2026:21381
https://access.redhat.com/errata/RHSA-2026:21382
https://access.redhat.com/errata/RHSA-2026:22325
https://access.redhat.com/errata/RHSA-2026:22643
https://access.redhat.com/errata/RHSA-2026:26174
https://access.redhat.com/errata/RHSA-2026:26268
https://access.redhat.com/errata/RHSA-2026:26269
https://access.redhat.com/errata/RHSA-2026:26270
https://access.redhat.com/errata/RHSA-2026:26491
https://access.redhat.com/errata/RHSA-2026:26492
https://access.redhat.com/errata/RHSA-2026:26493
https://access.redhat.com/errata/RHSA-2026:26521
https://access.redhat.com/errata/RHSA-2026:26536
https://access.redhat.com/errata/RHSA-2026:26539
https://access.redhat.com/errata/RHSA-2026:26551
https://access.redhat.com/errata/RHSA-2026:26606
https://access.redhat.com/errata/RHSA-2026:26629
https://access.redhat.com/errata/RHSA-2026:26630
https://access.redhat.com/errata/RHSA-2026:27715
https://access.redhat.com/security/cve/CVE-2026-8391
https://bugzilla.redhat.com/show_bug.cgi?id=2476475
https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-8391.json
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