CVE-2023-5941
📋 TL;DR
A heap buffer overflow vulnerability in FreeBSD's libc stdio function __sflush() allows attackers to corrupt data or execute arbitrary code when write errors occur. This affects applications using stdio functions on vulnerable FreeBSD versions. The vulnerability is critical with a CVSS score of 9.8.
💻 Affected Systems
- FreeBSD
📦 What is this software?
Freebsd by Freebsd
Freebsd by Freebsd
Freebsd by Freebsd
Freebsd by Freebsd
Freebsd by Freebsd
Freebsd by Freebsd
Freebsd by Freebsd
Freebsd by Freebsd
Freebsd by Freebsd
Freebsd by Freebsd
Freebsd by Freebsd
Freebsd by Freebsd
Freebsd by Freebsd
Freebsd by Freebsd
Freebsd by Freebsd
Freebsd by Freebsd
⚠️ Risk & Real-World Impact
Worst Case
Remote code execution leading to complete system compromise at the privilege level of the vulnerable application.
Likely Case
Application crashes, denial of service, or data corruption in affected programs.
If Mitigated
Limited impact if applications don't use stdio write-buffered streams or have proper error handling.
🎯 Exploit Status
Exploitation requires triggering write errors in stdio functions, which may be possible through network input or resource exhaustion.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: FreeBSD 12.4-RELEASE-p7 and FreeBSD 13.2-RELEASE-p5
Vendor Advisory: https://security.freebsd.org/advisories/FreeBSD-SA-23:15.stdio.asc
Restart Required: Yes
Instructions:
1. Update FreeBSD using 'freebsd-update fetch' and 'freebsd-update install'. 2. Rebuild and reinstall any third-party software linked against libc. 3. Reboot the system.
🔧 Temporary Workarounds
Disable write buffering
allSet buffering mode to unbuffered for stdio streams in applications
setvbuf(stream, NULL, _IONBF, 0);
🧯 If You Can't Patch
- Restrict network access to affected systems and applications
- Implement strict input validation and error handling in applications using stdio
🔍 How to Verify
Check if Vulnerable:
Check FreeBSD version with 'uname -a' and compare against affected versionsCheck Version:
uname -aVerify Fix Applied:
Verify version is 12.4-RELEASE-p7 or later, or 13.2-RELEASE-p5 or later📡 Detection & Monitoring
Log Indicators:
- Application crashes with segmentation faults
- Unexpected stdio error messages
- Core dumps from libc-related processes
Network Indicators:
- Unusual network traffic to applications using stdio functions
SIEM Query:
source="*freebsd*" AND (event="segmentation fault" OR event="core dumped") AND process="*libc*"