CVE-2025-24326: F5 BIG-IP ASM DoS Vulnerability

CVE-2025-24326 Overview

CVE-2025-24326 affects F5 BIG-IP Advanced WAF and ASM when the Behavioral DoS (BADoS) TLS Signatures feature is configured. Undisclosed network traffic can trigger an increase in memory resource utilization on the device. The condition results in a denial of service against the affected BIG-IP system.

F5 published the advisory on February 5, 2025, and assigned the issue to CWE-787. The vulnerability is remotely reachable, requires no authentication, and no user interaction. Software versions that reached End of Technical Support (EoTS) were not evaluated by the vendor.

Critical Impact

A remote, unauthenticated attacker can exhaust memory on BIG-IP systems with BADoS TLS Signatures enabled, disrupting the availability of protected applications.

Affected Products

• F5 BIG-IP Advanced WAF (Web Application Firewall)
• F5 BIG-IP Application Security Manager (ASM)
• BIG-IP deployments with the Behavioral DoS (BADoS) TLS Signatures feature configured

Discovery Timeline

• 2025-02-05 - CVE-2025-24326 published to the NVD
• 2025-08-08 - Last updated in NVD database

Technical Details for CVE-2025-24326

Vulnerability Analysis

The vulnerability resides in the Behavioral DoS (BADoS) TLS Signatures feature of BIG-IP Advanced WAF and ASM. BADoS performs behavioral analysis of TLS client signatures to identify and mitigate volumetric and application-layer denial of service attacks. When this feature is enabled, specific undisclosed traffic patterns cause memory utilization on the BIG-IP to grow.

NIST mapped the underlying weakness to CWE-787 (Out-of-bounds Write). Sustained memory growth on BIG-IP systems can degrade traffic processing, impact other modules sharing system memory, and ultimately reduce availability for applications behind the WAF. The vendor advisory characterizes the impact as availability-only with no confidentiality or integrity compromise.

Root Cause

The root cause is improper memory handling inside the BADoS TLS Signatures processing path. Specific traffic crafted against the TLS signature engine fails to release allocated memory or writes beyond intended buffer bounds, leading to abnormal growth in resident memory. F5 has not disclosed the exact triggering traffic to limit weaponization.

Attack Vector

The attack vector is network-based. An attacker sends crafted TLS traffic to a virtual server protected by BIG-IP Advanced WAF or ASM with BADoS TLS Signatures enabled. No credentials, configuration changes, or user interaction are required on the target device. Repeated requests amplify memory pressure until the system can no longer serve traffic reliably.

No public proof-of-concept, exploit module, or evidence of in-the-wild exploitation has been published. The issue is not listed in the CISA Known Exploited Vulnerabilities catalog.

Detection Methods for CVE-2025-24326

Indicators of Compromise

• Sustained or stepwise growth in tmm (Traffic Management Microkernel) memory utilization on BIG-IP devices with BADoS TLS Signatures enabled.
• BIG-IP system logs reporting memory pressure, tmm restarts, or BADoS module warnings without a corresponding traffic volume spike.
• Unexpected TLS handshake patterns or repeated client hellos directed at virtual servers protected by Advanced WAF/ASM.

Detection Strategies

• Baseline normal memory consumption for tmm and BADoS processes, then alert on deviations exceeding the baseline by a defined threshold.
• Correlate BIG-IP SNMP memory counters with WAF traffic logs to identify memory growth that is not explained by legitimate request volume.
• Inspect TLS client telemetry on upstream load balancers or network sensors for malformed or atypical handshake patterns targeting WAF-fronted virtual servers.

Monitoring Recommendations

• Forward BIG-IP /var/log/ltm, /var/log/asm, and SNMP host resource metrics to a centralized analytics platform for long-term trending.
• Configure alerting on tmm memory above operational thresholds and on any BADoS subsystem error messages.
• Monitor application availability behind the WAF for latency or 5xx response increases that coincide with memory anomalies on the BIG-IP.

How to Mitigate CVE-2025-24326

Immediate Actions Required

• Review the F5 Knowledge Base Article K000140950 to identify which installed BIG-IP versions are affected and which fixed versions are available.
• Upgrade affected BIG-IP Advanced WAF and ASM instances to a fixed software release published by F5.
• Verify whether the BADoS TLS Signatures feature is enabled on any virtual server, and inventory exposure accordingly.

Patch Information

F5 has published remediation guidance in K000140950. Customers should consult the advisory for the list of fixed branches and apply the corresponding upgrade path for their deployment. Software versions that have reached End of Technical Support were not evaluated and should be migrated to a supported release.

Workarounds

• Disable the BADoS TLS Signatures feature on affected virtual servers if patching cannot be performed immediately, accepting the loss of that specific protection layer.
• Place rate-limiting controls or upstream DDoS mitigation in front of BIG-IP virtual servers to reduce exposure to abusive TLS traffic.
• Restrict access to management and data-plane interfaces using network ACLs where business requirements allow.

# Check BADoS configuration and memory usage on BIG-IP
tmsh list security dos profile | grep -A5 tls-signatures
tmsh show sys memory
tmsh show sys proc-info tmm