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CVE-2025-11712: A malicious page could have used the type attribute of an OBJECT tag to override the default browser behavior

24
Routine
MEDIUM 6.1UPGRADEUPGRADE

CVE-2025-11712 is a medium-severity flaw (CVSS 6.1) affecting firefox, thunderbird. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

A malicious page could have used the type attribute of an OBJECT tag to override the default browser behavior when encountering a web resource served without a content-type. This could have contributed to an XSS on a site that unsafely serves files without a content-type header. This vulnerability was fixed in Firefox 144, Firefox ESR 140.4, Thunderbird 144, and Thunderbird 140.4.

Why this priority

  • No elevated risk signals yet

A fixed release or distro patch exists.

Risk facts

CVSS score6.1 (Medium)
Attack vectorNetwork (remote)
Attack complexityLow
Privileges neededNone
User interactionRequired
EPSS exploit chance0.2% (top 88%)
CISA exploited listNo
WeaknessCWE-116
Published2025-10-14
Last modified2026-10-23
Publisher (CNA): Mozilla Corporation · Vendor: mozilla

Am I affected?

Timeline

mozilla firefox UPGRADE
Affected: < 140.4.0 · < 144.0
Fixed in: 140.4.0, 144.0
Safe to downgrade to: no unaffected older release
1. Check installed version
apt-cache policy firefox || rpm -q firefox || firefox --version
2. UPGRADE to 140.4.0 (Debian / Ubuntu)
sudo apt update && sudo apt install --only-upgrade firefox
2. UPGRADE (RHEL / Amazon Linux / Fedora)
sudo dnf upgrade firefox
Note
Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.
mozilla thunderbird UPGRADE
Affected: < 140.4.0 · >= 141.0 and < 144.0
Fixed in: 140.4.0, 144.0
Safe to downgrade to: a release before 141.0
1. Check installed version
apt-cache policy thunderbird || rpm -q thunderbird || thunderbird --version
2. UPGRADE to 140.4.0 (Debian / Ubuntu)
sudo apt update && sudo apt install --only-upgrade thunderbird
2. UPGRADE (RHEL / Amazon Linux / Fedora)
sudo dnf upgrade thunderbird
Note
Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.
3. If no update is available yet, DOWNGRADE to a release before 141.0 (Debian / Ubuntu)
apt-cache madison thunderbird sudo apt install thunderbird=<VERSION_BEFORE_141.0> sudo apt-mark hold thunderbird
3. If no update is available yet, DOWNGRADE (RHEL / Amazon Linux / Fedora)
dnf --showduplicates list thunderbird sudo dnf downgrade thunderbird-<VERSION_BEFORE_141.0> sudo dnf versionlock add thunderbird
Downgrade risk
Downgrading can break dependent software and may reopen older bugs. Read the distro advisory first and test on a non-production host.
After downgrade
Restart the service, and keep the package held until a fixed release ships.
Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2025-11712?

firefox: upgrade to 140.4.0, 144.0; thunderbird: upgrade to 140.4.0, 144.0. Exact commands for each OS are on this page.

Is CVE-2025-11712 being exploited?

CVE-2025-11712 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2025-11712 affect?

CVE-2025-11712 affects firefox, thunderbird. Severity is medium (CVSS 6.1). A malicious page could have used the type attribute of an OBJECT tag to override the default browser behavior when encountering a web resource served without a content-type. This could have contributed to an XSS on a site that unsafely serv

How urgent is CVE-2025-11712?

Priority 24/100. No elevated risk signals yet.

Software pages

Mozilla Firefox vulnerabilities

Related CVEs

References

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