CVE-2021-44538
📋 TL;DR
A buffer overflow vulnerability in Matrix libolm's olm_session_describe function allows remote attackers to execute arbitrary code or cause denial of service by sending crafted messages. The vulnerability affects applications using libolm for end-to-end encryption, particularly Element Web and SchildiChat Web. Attackers can partially control overflow content using ASCII spaces and digits.
💻 Affected Systems
- Element Web
- SchildiChat Web
- Any application using libolm
📦 What is this software?
Cinny by Cinny Project
Element by Matrix
Element by Matrix
Olm by Matrix
Schildichat by Schildi
Schildichat by Schildi
⚠️ Risk & Real-World Impact
Worst Case
Remote code execution leading to complete system compromise, data theft, or ransomware deployment on affected systems.
Likely Case
Denial of service crashes in Matrix clients, potentially disrupting secure communications and causing service interruptions.
If Mitigated
Limited impact with proper input validation and memory protections, potentially reduced to application crashes without code execution.
🎯 Exploit Status
Exploitation requires constructing specific message sequences to manipulate session state, but remote attackers can trigger the vulnerability without authentication.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: libolm 3.2.7 and later
Vendor Advisory: https://matrix.org/blog/2021/12/13/disclosure-buffer-overflow-in-libolm-and-matrix-js-sdk
Restart Required: Yes
Instructions:
1. Update libolm to version 3.2.7 or later. 2. Update any dependent applications (Element Web, SchildiChat Web). 3. Restart affected services and applications.
🔧 Temporary Workarounds
Disable vulnerable functionality
allTemporarily disable olm_session_describe calls or restrict access to Matrix services
🧯 If You Can't Patch
- Implement network segmentation to isolate vulnerable systems from untrusted networks
- Deploy application firewalls with buffer overflow protection rules
🔍 How to Verify
Check if Vulnerable:
Check libolm version: dpkg -l | grep libolm or check package manager for version < 3.2.7Check Version:
pkg-config --modversion olmVerify Fix Applied:
Confirm libolm version is 3.2.7 or later and verify application functionality📡 Detection & Monitoring
Log Indicators:
- Application crashes with segmentation faults
- Unusual memory access patterns in system logs
- Abnormal termination of Matrix client processes
Network Indicators:
- Unusual message sequences in Matrix protocol traffic
- Malformed cryptographic session initialization attempts
SIEM Query:
source="*matrix*" AND (event="segmentation fault" OR event="buffer overflow" OR event="access violation")🔗 References
- https://gitlab.matrix.org/matrix-org/olm/-/tags
- https://lists.debian.org/debian-lts-announce/2022/01/msg00001.html
- https://matrix.org/blog/2021/12/13/disclosure-buffer-overflow-in-libolm-and-matrix-js-sdk
- https://www.debian.org/security/2022/dsa-5034
- https://gitlab.matrix.org/matrix-org/olm/-/tags
- https://lists.debian.org/debian-lts-announce/2022/01/msg00001.html
- https://matrix.org/blog/2021/12/13/disclosure-buffer-overflow-in-libolm-and-matrix-js-sdk
- https://www.debian.org/security/2022/dsa-5034
