CVE-2021-3697
📋 TL;DR
CVE-2021-3697 is a heap buffer underflow vulnerability in GRUB2's JPEG parser that allows a crafted JPEG image to corrupt heap memory. Successful exploitation could lead to arbitrary code execution or secure boot circumvention. This affects systems using GRUB2 versions prior to 2.12 for booting.
💻 Affected Systems
- GRUB2
📦 What is this software?
Enterprise Linux For Power Little Endian by Redhat
View all CVEs affecting Enterprise Linux For Power Little Endian →
Enterprise Linux For Power Little Endian by Redhat
View all CVEs affecting Enterprise Linux For Power Little Endian →
Enterprise Linux For Power Little Endian Eus by Redhat
View all CVEs affecting Enterprise Linux For Power Little Endian Eus →
Enterprise Linux For Power Little Endian Eus by Redhat
View all CVEs affecting Enterprise Linux For Power Little Endian Eus →
Enterprise Linux For Power Little Endian Eus by Redhat
View all CVEs affecting Enterprise Linux For Power Little Endian Eus →
Enterprise Linux For Power Little Endian Eus by Redhat
View all CVEs affecting Enterprise Linux For Power Little Endian Eus →
Openshift by Redhat
⚠️ Risk & Real-World Impact
Worst Case
Full system compromise via arbitrary code execution during boot, potentially bypassing secure boot protections and gaining persistent access.
Likely Case
System instability, data corruption, or denial of service during boot process, requiring physical intervention to recover.
If Mitigated
Limited impact due to exploit complexity and requirement for attacker to control boot media or EFI system partition.
🎯 Exploit Status
Exploitation requires precise heap manipulation and control over boot media. Attackers need physical access or ability to modify EFI system partition.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: grub-2.12 and later
Vendor Advisory: https://bugzilla.redhat.com/show_bug.cgi?id=1991687
Restart Required: Yes
Instructions:
1. Update GRUB2 package to version 2.12 or later using distribution package manager. 2. Regenerate GRUB configuration with 'grub-mkconfig' or 'update-grub'. 3. Reboot system to load patched GRUB.
🔧 Temporary Workarounds
Disable JPEG support in GRUB
linuxRemove JPEG module loading to prevent vulnerability trigger
Remove 'jpeg' from GRUB modules in /etc/default/grub
Run: update-grub
Use text-only boot
linuxDisable graphical boot splash entirely
Set GRUB_TERMINAL=console in /etc/default/grub
Remove GRUB_THEME settings
Run: update-grub
🧯 If You Can't Patch
- Restrict physical access to systems and secure boot media
- Implement secure boot with trusted certificates only
🔍 How to Verify
Check if Vulnerable:
Check GRUB version with: grub-install --version | grep -o '2\.[0-9]*'Check Version:
grub-install --versionVerify Fix Applied:
Verify GRUB version is 2.12 or higher and check that 'jpeg' module is not loaded in GRUB configuration📡 Detection & Monitoring
Log Indicators:
- GRUB boot failures
- Kernel panic during early boot
- Unexpected modifications to /boot/grub files
Network Indicators:
- None - local exploit only
SIEM Query:
Search for: 'grub' AND ('failed' OR 'panic' OR 'corruption') in boot logs🔗 References
- https://bugzilla.redhat.com/show_bug.cgi?id=1991687
- https://security.gentoo.org/glsa/202209-12
- https://security.netapp.com/advisory/ntap-20220930-0001/
- https://bugzilla.redhat.com/show_bug.cgi?id=1991687
- https://security.gentoo.org/glsa/202209-12
- https://security.netapp.com/advisory/ntap-20220930-0001/
