CVE-2025-5271 | Devtools' preview ignored CSP headers

Previewing a response in Devtools ignored CSP headers, which could have allowed content injection attacks. This vulnerability was fixed in Firefox 139 and Thunderbird 139.

Published: 2025-05-27 Last update: 2026-04-13 Assigner: [email protected] Source: [email protected]
NVD Status：Modified，CVE State: published
View at NVD, CVE.org, EUVD

CVE-2025-5271 is rated Moderate Risk (44.2/100): CVSS Medium severity, with medium exploitation likelihood (EPSS 0.28%). 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-2025-5271

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 2026-03-23 0.05% 0.28% +0.23%
2 2025-11-04 0.05% 0.05% +0.01%
3 2025-10-23 — 0.05% —

Full EPSS history (5 records total)

Common vulnerability scoring system (CVSS) metrics for CVE-2025-5271

CVSS metrics for this CVE.

Base score Version Severity Vector Exploitability Impact Score source
6.5 3.1 MEDIUM
CVSS:3.1/AV:N/AC:L/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: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:L)
Attackers could change some data, but it’s limited—not everything goes.
Availability (A:N)
Service keeps running; no real outage angle.
 3.9 2.5 134c704f-9b21-4f2e-91b3-4a467353bcc0

Weakness enumeration for CVE-2025-5271

OS Trackers for CVE-2025-5271

vendor priority summary link
alpine — CVE-2025-5271: 1 source package rows (firefox); 145 state rows across 2 repos (3.22-community, edge-community); fixed 0, open 145. https://security.alpinelinux.org/vuln/CVE-2025-5271
debian not yet assigned CVE-2025-5271 not yet assigned priority: Debian including 1 source packages (firefox), 1 status rows across 1 suites (sid): resolved 1. https://security-tracker.debian.org/tracker/CVE-2025-5271
redhat low — https://access.redhat.com/security/cve/CVE-2025-5271
suse high — https://www.suse.com/security/cve/CVE-2025-5271/
ubuntu medium CVE-2025-5271 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, needs-triage 9, not-affected 9, released 2. https://ubuntu.com/security/CVE-2025-5271

Affected software / configurations for CVE-2025-5271

Vendor Product Version Raw CPE
mozilla firefox < 139.0 cpe:2.3:a:mozilla:firefox:*:*:*:*:*:*:*:*

References for CVE-2025-5271

cvelogic Threat Intelligence