CVE-2025-43857
📋 TL;DR
This vulnerability in Ruby's Net::IMAP library allows a malicious or compromised IMAP server to cause denial of service through memory exhaustion. When connecting to untrusted servers, the client automatically allocates memory based on server-provided byte counts without validation, potentially consuming all available memory. This affects Ruby applications using vulnerable Net::IMAP versions to connect to IMAP servers.
💻 Affected Systems
- Ruby net-imap gem
📦 What is this software?
Net\ by Ruby Lang
Net\ by Ruby Lang
Net\ by Ruby Lang
Net\ by Ruby Lang
⚠️ Risk & Real-World Impact
Worst Case
Complete system memory exhaustion leading to application crash, service disruption, and potential system instability affecting other services on the same host.
Likely Case
Application memory exhaustion causing IMAP client functionality to fail, potentially disrupting email synchronization or IMAP-dependent services.
If Mitigated
Minimal impact when connecting only to trusted, well-behaved IMAP servers with proper network segmentation and monitoring.
🎯 Exploit Status
Exploitation requires a malicious server or compromised legitimate server. No authentication needed as the attack occurs during normal IMAP protocol communication.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 0.5.7, 0.4.20, 0.3.9, or 0.2.5 depending on your version series
Vendor Advisory: https://github.com/ruby/net-imap/security/advisories
Restart Required: Yes
Instructions:
1. Identify which net-imap version series you're using (0.5.x, 0.4.x, 0.3.x, or 0.2.x). 2. Update to the patched version for your series: 'gem update net-imap' or update your Gemfile to specify the patched version. 3. Restart your Ruby application to load the updated gem.
🔧 Temporary Workarounds
Restrict IMAP server connections
allOnly allow connections to trusted, known-good IMAP servers. Implement allowlisting of IMAP server endpoints.
Implement connection monitoring and limits
linuxMonitor memory usage of Ruby processes using Net::IMAP and implement process memory limits.
ulimit -v [memory_limit_in_kb] # For Linux process memory limit
🧯 If You Can't Patch
- Implement strict network controls to only allow connections to trusted IMAP servers
- Monitor application memory usage and implement automatic restart thresholds
🔍 How to Verify
Check if Vulnerable:
Check your net-imap gem version: 'gem list net-imap' or check Gemfile.lock for net-imap versionCheck Version:
gem list net-imapVerify Fix Applied:
Verify net-imap version is 0.5.7, 0.4.20, 0.3.9, or 0.2.5 or higher: 'gem list net-imap | grep -E "0\.5\.7|0\.4\.20|0\.3\.9|0\.2\.5"'📡 Detection & Monitoring
Log Indicators:
- Sudden increase in Ruby application memory usage
- Application crashes or restarts related to memory exhaustion
- IMAP connection failures to untrusted servers
Network Indicators:
- Connections to non-standard or unexpected IMAP servers
- Unusually large IMAP literal size indicators in network traffic
SIEM Query:
source="application_logs" ("out of memory" OR "memory allocation failed") AND process="ruby" AND "net-imap"🔗 References
- https://github.com/ruby/net-imap/pull/442
- https://github.com/ruby/net-imap/pull/444/commits/0ae8576c1a90bcd9573f81bdad4b4b824642d105#diff-53721cb4d9c3fb86b95cc8476ca2df90968ad8c481645220c607034399151462
- https://github.com/ruby/net-imap/pull/445
- https://github.com/ruby/net-imap/pull/446
- https://github.com/ruby/net-imap/pull/447
- https://github.com/ruby/net-imap/security/advisories/GHSA-j3g3-5qv5-52mj
