CVE-2025-10532: Mozilla Firefox Buffer Overflow Vulnerability

CVE-2025-10532 Overview

CVE-2025-10532 is a boundary condition flaw in the JavaScript garbage collector (GC) component of Mozilla Firefox and Thunderbird. The issue affects memory management routines invoked by the JavaScript engine and can be triggered through web content rendered in the browser. Mozilla resolved the vulnerability in Firefox 143, Firefox ESR 140.3, Thunderbird 143, and Thunderbird 140.3. The weakness is classified under [CWE-754] (Improper Check for Unusual or Exceptional Conditions). Remote attackers can reach the affected code paths without authentication or user interaction by serving crafted JavaScript to a vulnerable client.

Critical Impact
Remote attackers can trigger incorrect boundary handling in the JavaScript GC component to compromise limited confidentiality and integrity within the browser process.

Affected Products

Mozilla Firefox versions prior to 143
Mozilla Firefox ESR versions prior to 140.3
Mozilla Thunderbird versions prior to 143 and 140.3

Discovery Timeline

2025-09-16 - CVE-2025-10532 published to NVD
2026-06-17 - Last updated in NVD database

Technical Details for CVE-2025-10532

Vulnerability Analysis

The vulnerability resides in the JavaScript engine's garbage collection (GC) subsystem within Gecko. The GC component performs boundary checks when tracking object references and reclaiming memory during collection cycles. Incorrect boundary conditions in these routines allow the engine to reach states that were not anticipated by the developers. Because the flaw is reachable over the network with no privileges or user interaction, any web page or HTML email rendered by the affected client can invoke the vulnerable code path. The impact is limited to partial confidentiality and integrity effects on the browser process, without direct availability degradation.

Root Cause

The root cause is an improper check for unusual or exceptional conditions [CWE-754] in boundary validation logic inside the JavaScript GC. Refer to Mozilla Bug Report #1979502 and the associated advisories for source-level details.

Attack Vector

Exploitation requires a victim to load attacker-controlled JavaScript in Firefox, Firefox ESR, or Thunderbird. In Thunderbird, remote content in HTML messages can supply the trigger. The attacker does not need credentials or elevated privileges. No verified proof-of-concept code is publicly available for CVE-2025-10532.

// No verified public exploit code is available for CVE-2025-10532.
// See the Mozilla Foundation Security Advisories (MFSA-2025-73, 75, 77, 78)
// and Bugzilla entry 1979502 for technical references.

Detection Methods for CVE-2025-10532

Indicators of Compromise

Firefox or Thunderbird process crashes or unexpected renderer restarts correlated with rendering untrusted web content or HTML email.
Outbound connections from browser processes to newly registered or low-reputation domains immediately following JavaScript-heavy page loads.
Client telemetry showing Firefox or Thunderbird versions below 143 (or ESR below 140.3) still in production use.

Detection Strategies

Inventory endpoints running Mozilla Firefox and Thunderbird and flag installations older than the fixed builds.
Monitor endpoint process telemetry for anomalous child process creation or memory anomalies originating from firefox.exe, firefox, or thunderbird binaries.
Correlate browser crash reports with URL access logs from web proxies to identify potential exploitation attempts.

Monitoring Recommendations

Ingest browser crash dumps and endpoint process events into a central SIEM for retrospective hunting.
Alert on connections to unpatched Firefox/Thunderbird user agents traversing the corporate proxy.
Track Mozilla advisories MFSA-2025-73, 75, 77, and 78 for supplementary fixes referencing the same GC component.

How to Mitigate CVE-2025-10532

Immediate Actions Required

Upgrade Firefox to version 143 or later and Firefox ESR to 140.3 or later on all managed endpoints.
Upgrade Thunderbird to version 143 or Thunderbird ESR 140.3 on all mail clients.
Apply distribution updates from Debian LTS announcements referenced in the Mozilla advisories.
Enforce automatic browser and mail client updates through endpoint management tooling.

Patch Information

Mozilla released fixes in Firefox 143, Firefox ESR 140.3, Thunderbird 143, and Thunderbird 140.3. Details are published in Mozilla Security Advisory MFSA-2025-73, MFSA-2025-75, MFSA-2025-77, and MFSA-2025-78. Debian users should apply updates from the Debian LTS Announcement #20 and Debian LTS Announcement #26.

Workarounds

Disable JavaScript for untrusted sites through enterprise browser policies if patching is delayed.
Block remote content in Thunderbird messages by default to prevent automatic script execution.
Restrict browsing to trusted domains via web proxy allowlists on high-risk hosts pending remediation.

bash

# Verify Firefox version on Linux endpoints
firefox --version

# Verify Thunderbird version
thunderbird --version

# Debian/Ubuntu update commands
sudo apt update
sudo apt install --only-upgrade firefox-esr thunderbird