CVE-2017-7476
📋 TL;DR
CVE-2017-7476 is a heap-based buffer overflow vulnerability in Gnulib's timezone handling code. Attackers can exploit this by manipulating the TZ environment variable to execute arbitrary code or cause denial of service. Systems using Gnulib before April 26, 2017 are affected.
💻 Affected Systems
- Gnulib
- Software using Gnulib components
📦 What is this software?
Gnulib by Gnulib
⚠️ Risk & Real-World Impact
Worst Case
Remote code execution leading to complete system compromise, data theft, or ransomware deployment.
Likely Case
Denial of service through application crashes or limited code execution in sandboxed environments.
If Mitigated
Minimal impact if systems are patched, isolated, or have memory protection mechanisms enabled.
🎯 Exploit Status
Exploitation requires control over TZ environment variable, which may be possible through various input vectors.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Gnulib 2017-04-26 or later
Vendor Advisory: http://git.savannah.gnu.org/gitweb/?p=gnulib.git%3Ba=commit%3Bh=94e01571507835ff59dd8ce2a0b56a4b566965a4
Restart Required: Yes
Instructions:
1. Update Gnulib to version 2017-04-26 or later. 2. Rebuild any applications using Gnulib. 3. Restart affected services.
🔧 Temporary Workarounds
Restrict TZ Environment Variable
linuxPrevent untrusted users from setting TZ environment variable
export TZ=""
unset TZ
Memory Protection
linuxEnable ASLR and other memory protection mechanisms
sysctl -w kernel.randomize_va_space=2
🧯 If You Can't Patch
- Isolate affected systems from untrusted networks
- Implement strict input validation for environment variables
🔍 How to Verify
Check if Vulnerable:
Check Gnulib version date or examine time_rz.c for the vulnerable save_abbr functionCheck Version:
grep -r "gnulib" /usr/include/ || find /usr -name "*.c" -exec grep -l "save_abbr" {} \;Verify Fix Applied:
Verify Gnulib version is 2017-04-26 or later and check commit 94e01571507835ff59dd8ce2a0b56a4b566965a4 is present📡 Detection & Monitoring
Log Indicators:
- Application crashes with segmentation faults
- Unexpected process termination
Network Indicators:
- Unusual TZ environment variable values in process execution
SIEM Query:
process where (command_line contains "TZ=" and command_line length > 100)🔗 References
- http://git.savannah.gnu.org/gitweb/?p=gnulib.git%3Ba=commit%3Bh=94e01571507835ff59dd8ce2a0b56a4b566965a4
- http://www.securityfocus.com/bid/98098
- https://bugzilla.redhat.com/show_bug.cgi?id=1444774
- https://bugzilla.redhat.com/show_bug.cgi?id=1445185
- https://security-tracker.debian.org/tracker/CVE-2017-7476
- http://git.savannah.gnu.org/gitweb/?p=gnulib.git%3Ba=commit%3Bh=94e01571507835ff59dd8ce2a0b56a4b566965a4
- http://www.securityfocus.com/bid/98098
- https://bugzilla.redhat.com/show_bug.cgi?id=1444774
- https://bugzilla.redhat.com/show_bug.cgi?id=1445185
- https://security-tracker.debian.org/tracker/CVE-2017-7476
