CVE-2025-5271Network attack vector

Content injection via CSP-bypassing response preview

Published May 27, 2025 · Updated Apr 13, 2026

Content injection in DevTools response preview in Mozilla Firefox and Thunderbird before 139 allows remote attackers to inject content. The preview renderer displays an HTTP response without enforcing its Content Security Policy headers, so policy-blocked content is processed in the preview context. A crafted response must be opened in DevTools preview; published sources do not specify the injected content's execution scope or resulting data access.

CVSS severity6.5
Medium
EPSS probability0.30%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Content injection in DevTools response preview in Mozilla Firefox and Thunderbird before 139 allows remote attackers to inject content. The preview renderer displays an HTTP response without enforcing its Content Security Policy headers, so policy-blocked content is processed in the preview context. A crafted response must be opened in DevTools preview; published sources do not specify the injected content's execution scope or resulting data access.

The record

CVE
CVE-2025-5271
Published
May 27, 2025
Updated
Apr 13, 2026
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-116
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. May 27, 2025CVE publishedPublication date reported by the CVE source.
  2. Apr 13, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Affected buildAffected product and version details are unavailable.

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Affected products and versions are unavailable in this record.

Published CVSS scores

6.5CISA-ADPCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

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No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-116Improper Encoding or Escaping of Output

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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