CVE-2023-25729
📋 TL;DR
This vulnerability allows Firefox/Thunderbird extensions to bypass permission prompts when opening external schemes (like file://, mailto:, etc.), enabling them to automatically download files or interact with installed software without user consent. It affects users running Firefox versions below 110, Thunderbird below 102.8, and Firefox ESR below 102.8.
💻 Affected Systems
- Mozilla Firefox
- Mozilla Thunderbird
- Mozilla Firefox ESR
📦 What is this software?
Firefox by Mozilla
Firefox Esr by Mozilla
Thunderbird by Mozilla
⚠️ Risk & Real-World Impact
Worst Case
Malicious extension could automatically download and execute malware, steal files, or interact with other applications to compromise the entire system.
Likely Case
Malicious extension could download unwanted files, open phishing links, or trigger unwanted application behavior without user awareness.
If Mitigated
With proper extension vetting and user caution, impact is limited to unwanted file downloads or application launches.
🎯 Exploit Status
Exploitation requires user to install a malicious extension, but once installed, no further user interaction is needed.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Firefox 110+, Thunderbird 102.8+, Firefox ESR 102.8+
Vendor Advisory: https://www.mozilla.org/security/advisories/mfsa2023-05/
Restart Required: Yes
Instructions:
1. Open Firefox/Thunderbird. 2. Click menu → Help → About Firefox/Thunderbird. 3. Allow automatic update to latest version. 4. Restart browser when prompted.
🔧 Temporary Workarounds
Disable unnecessary extensions
allRemove or disable extensions that aren't essential, especially from untrusted sources.
Use extension allowlisting
allConfigure browser to only allow approved extensions from trusted sources.
🧯 If You Can't Patch
- Restrict installation of browser extensions to trusted sources only.
- Monitor for unexpected file downloads or external application launches.
🔍 How to Verify
Check if Vulnerable:
Check browser version in About dialog. If Firefox < 110, Thunderbird < 102.8, or Firefox ESR < 102.8, system is vulnerable.Check Version:
firefox --version (Linux) or check About Firefox in GUIVerify Fix Applied:
Confirm version is Firefox ≥ 110, Thunderbird ≥ 102.8, or Firefox ESR ≥ 102.8 after update.📡 Detection & Monitoring
Log Indicators:
- Unexpected external scheme launches (file://, mailto:) without user prompts
- Extension activity logs showing permission bypass
Network Indicators:
- Unexpected downloads from browser without user interaction
SIEM Query:
source="browser_logs" AND (event="external_scheme_launch" OR event="permission_bypass")🔗 References
- https://bugzilla.mozilla.org/show_bug.cgi?id=1792138
- https://www.mozilla.org/security/advisories/mfsa2023-05/
- https://www.mozilla.org/security/advisories/mfsa2023-06/
- https://www.mozilla.org/security/advisories/mfsa2023-07/
- https://bugzilla.mozilla.org/show_bug.cgi?id=1792138
- https://www.mozilla.org/security/advisories/mfsa2023-05/
- https://www.mozilla.org/security/advisories/mfsa2023-06/
- https://www.mozilla.org/security/advisories/mfsa2023-07/
- https://bugzilla.mozilla.org/show_bug.cgi?id=1792138
