CVE-2025-53521
📋 TL;DR
This vulnerability in BIG-IP APM allows undisclosed traffic to cause TMM (Traffic Management Microkernel) to terminate when an Access Policy is configured. This affects BIG-IP systems running vulnerable versions with APM Access Policies enabled. The TMM termination results in service disruption for traffic handled by the affected virtual server.
💻 Affected Systems
- F5 BIG-IP with APM module
📦 What is this software?
Big Ip Advanced Web Application Firewall by F5
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Big Ip Advanced Web Application Firewall by F5
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Big Ip Advanced Web Application Firewall by F5
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Big Ip Advanced Web Application Firewall by F5
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Big Ip Application Acceleration Manager by F5
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Big Ip Application Acceleration Manager by F5
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Big Ip Application Acceleration Manager by F5
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Big Ip Application Acceleration Manager by F5
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Big Ip Application Security Manager by F5
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Big Ip Application Security Manager by F5
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Big Ip Application Security Manager by F5
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Big Ip Application Security Manager by F5
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Big Ip Application Visibility And Reporting by F5
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Big Ip Application Visibility And Reporting by F5
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Big Ip Application Visibility And Reporting by F5
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⚠️ Risk & Real-World Impact
Worst Case
Complete denial of service for all traffic passing through the affected virtual server, potentially affecting multiple applications and services.
Likely Case
Intermittent service disruption as TMM restarts, causing connection drops and temporary unavailability of applications behind the APM policy.
If Mitigated
Limited impact to single virtual server if proper segmentation and redundancy are in place.
🎯 Exploit Status
Undisclosed traffic suggests unauthenticated network traffic can trigger the vulnerability. No public exploit details available.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Refer to F5 advisory K000156741 for specific fixed versions
Vendor Advisory: https://my.f5.com/manage/s/article/K000156741
Restart Required: Yes
Instructions:
1. Review F5 advisory K000156741 for affected versions. 2. Upgrade to fixed version per F5 documentation. 3. Restart TMM services after patching. 4. Verify APM functionality post-upgrade.
🔧 Temporary Workarounds
Disable APM Access Policy
allRemove or disable APM Access Policy from vulnerable virtual servers
tmsh modify ltm virtual <virtual_server_name> policies remove { <apm_policy_name> }
Implement Network Controls
allRestrict access to vulnerable virtual servers using firewall rules
🧯 If You Can't Patch
- Implement strict network segmentation to limit access to vulnerable virtual servers
- Monitor TMM process health and implement automated restart procedures
🔍 How to Verify
Check if Vulnerable:
Check if BIG-IP version is listed as vulnerable in F5 advisory K000156741 and verify APM Access Policy configuration on virtual serversCheck Version:
tmsh show sys versionVerify Fix Applied:
Verify BIG-IP version is updated to fixed version and test APM functionality with simulated traffic📡 Detection & Monitoring
Log Indicators:
- TMM process termination/restart events in /var/log/ltm
- APM policy failure logs
- Increased TMM restart frequency
Network Indicators:
- Unexpected traffic patterns to APM-configured virtual servers
- Service disruption events correlated with specific traffic
SIEM Query:
source="bigip.log" AND ("TMM terminated" OR "TMM restart" OR "apm policy error")