CVE-2025-3032 Overview
CVE-2025-3032 affects Mozilla Firefox and Mozilla Thunderbird on Unix-like systems. The fork server leaks file descriptors into web content processes, breaking the sandbox isolation boundary. A compromised content process can inherit these descriptors and use them to escalate privileges within the browser architecture. Mozilla classifies this as an issue mapped to CWE-403: Exposure of File Descriptor to Unintended Control Sphere. Mozilla fixed the flaw in Firefox 137 and Thunderbird 137, as documented in Mozilla Security Advisory MFSA-2025-20 and Mozilla Security Advisory MFSA-2025-23.
Critical Impact
A successfully exploited content process can leverage leaked file descriptors to escape sandbox restrictions and escalate privileges within the browser.
Affected Products
- Mozilla Firefox versions prior to 137
- Mozilla Thunderbird versions prior to 137
- Unix-like platforms using the Firefox fork server architecture
Discovery Timeline
- 2025-04-01 - CVE-2025-3032 published to NVD
- 2026-04-13 - Last updated in NVD database
Technical Details for CVE-2025-3032
Vulnerability Analysis
Firefox uses a multi-process architecture that separates privileged parent processes from sandboxed web content processes. On Unix-like platforms, a fork server creates content processes efficiently by forking from a pre-initialized template. This design reduces process startup latency but introduces shared state risks.
The vulnerability stems from file descriptors that the fork server retained when spawning web content processes. These descriptors should have been closed or sanitized before the child process executed untrusted web content. Inherited descriptors expose resources outside the intended sandbox boundary, which violates the principle of least privilege.
An attacker who first achieves code execution inside a content process — through a separate renderer flaw — can then access the leaked descriptors. Depending on what the descriptors reference, the attacker may read or write privileged resources, bypass sandbox restrictions, or escalate privileges within the browser process tree. The attack complexity is rated High because it requires chaining with a prior content-process compromise.
Root Cause
The root cause is improper management of inheritable file descriptors in the fork server. The server did not close or mark all sensitive descriptors as close-on-exec before transitioning into the web content sandbox. This falls under CWE-403: Exposure of File Descriptor to Unintended Control Sphere.
Attack Vector
Exploitation occurs over the network through a malicious web page. The attacker must first compromise the content process using a separate vulnerability. The leaked file descriptors then provide handles that the compromised renderer can use against resources normally outside its sandbox. Refer to Mozilla Bug Report #1949987 for the underlying tracking record.
No verified public exploit code or proof-of-concept is available for this issue.
Detection Methods for CVE-2025-3032
Indicators of Compromise
- Firefox or Thunderbird content processes accessing file descriptors that point to parent-process or system resources outside the sandbox.
- Unexpected child processes spawned by firefox or thunderbird binaries on Linux endpoints running pre-137 builds.
- Crash reports or dmesg entries referencing sandbox policy violations from web content processes.
Detection Strategies
- Inventory installed Firefox and Thunderbird versions across managed endpoints and flag any build below 137.
- Monitor process telemetry for content processes performing syscalls inconsistent with renderer behavior, such as openat against privileged paths.
- Correlate browser crash telemetry with sandbox escape indicators from EDR process trees.
Monitoring Recommendations
- Track Mozilla advisory feeds for follow-up issues related to MFSA-2025-20 and MFSA-2025-23.
- Alert on Firefox or Thunderbird processes opening sockets, devices, or files atypical for renderer workloads.
- Audit endpoint compliance reports weekly to confirm browser patch rollout completion.
How to Mitigate CVE-2025-3032
Immediate Actions Required
- Upgrade Mozilla Firefox to version 137 or later on all endpoints.
- Upgrade Mozilla Thunderbird to version 137 or later on all mail clients.
- Confirm enterprise update channels (ESR, rapid release) include the fixed builds before broad deployment.
Patch Information
Mozilla addressed CVE-2025-3032 in Firefox 137 and Thunderbird 137. Patch details are published in Mozilla Security Advisory MFSA-2025-20 and Mozilla Security Advisory MFSA-2025-23. Administrators should validate version strings using firefox --version and thunderbird --version after deployment.
Workarounds
- No vendor-supplied workaround exists; patching is the supported remediation.
- Restrict browsing to trusted sites and disable JavaScript in high-risk contexts until patches are applied.
- Apply operating system-level sandbox hardening, such as seccomp-bpf and AppArmor profiles, to reduce blast radius from a compromised renderer.
# Verify patched browser versions on Linux endpoints
firefox --version
thunderbird --version
# Expected output should report version 137 or later
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
