CVE-2025-4087 | Unsafe attribute access during XPath parsing

A vulnerability was identified in Thunderbird where XPath parsing could trigger undefined behavior due to missing null checks during attribute access. This could lead to out-of-bounds read access and potentially, memory corruption. This vulnerability was fixed in Firefox 138, Firefox ESR 128.10, Thunderbird 138, and Thunderbird 128.10.

Published: 2025-04-29 Last update: 2026-04-13 Assigner: [email protected] Source: [email protected]
NVD Status：Modified，CVE State: published
View at NVD, CVE.org, EUVD

CVE-2025-4087 is rated Moderate Risk (41.5/100): CVSS Medium severity, with medium exploitation likelihood (EPSS 0.44%). Review affected assets and schedule remediation.

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-2025-4087

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 2026-02-23 0.05% 0.44% +0.39%
2 2025-10-07 0.04% 0.05% +0.01%
3 2025-09-25 — 0.04% —

Full EPSS history (5 records total)

Common vulnerability scoring system (CVSS) metrics for CVE-2025-4087

CVSS metrics for this CVE.

Base score Version Severity Vector Exploitability Impact Score source
4.8 3.1 MEDIUM
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/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: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: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:L)
Attackers could change some data, but it’s limited—not everything goes.
Availability (A:N)
Service keeps running; no real outage angle.
 2.2 2.5 134c704f-9b21-4f2e-91b3-4a467353bcc0

Weakness enumeration for CVE-2025-4087

OS Trackers for CVE-2025-4087

vendor priority summary link
alpine — CVE-2025-4087: 3 source package rows (firefox, firefox-esr, thunderbird); 353 state rows across 2 repos (3.22-community, edge-community); fixed 0, open 353. https://security.alpinelinux.org/vuln/CVE-2025-4087
debian not yet assigned CVE-2025-4087 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-2025-4087
redhat medium — https://access.redhat.com/security/cve/CVE-2025-4087
suse high CVE-2025-4087 severity important: SUSE including 23 source package names (MozillaFirefox-128.10.0-150200.152.179.1, MozillaFirefox-138.0-1.1, …), 105 product×package rows across 38 product lines (Container suse/kiosk/firefox-esr, Image SLES15-SP3-SAP-Azure-LI-BYOS-Production, … (38 product lines)): Fixed 105. https://www.suse.com/security/cve/CVE-2025-4087/
ubuntu medium CVE-2025-4087 medium priority: Ubuntu including 9 source packages (firefox, mozjs102, …), 65 status rows across 8 suites (bionic, focal, jammy, noble, oracular, plucky, questing, upstream): DNE 35, ignored 10, not-affected 9, needs-triage 8, released 3. https://ubuntu.com/security/CVE-2025-4087

Affected software / configurations for CVE-2025-4087

Vendor Product Version Raw CPE
mozilla firefox < 128.10 cpe:2.3:a:mozilla:firefox:*:*:*:*:esr:*:*:*
mozilla firefox < 138.0 cpe:2.3:a:mozilla:firefox:*:*:*:*:-:*:*:*
mozilla thunderbird < 128.10.0 cpe:2.3:a:mozilla:thunderbird:*:*:*:*:esr:*:*:*
mozilla thunderbird < 138.0 cpe:2.3:a:mozilla:thunderbird:*:*:*:*:-:*:*:*

References for CVE-2025-4087

cvelogic Threat Intelligence