New Snort rule addresses critical vulnerability in F5 BIG

CVE-2020-5902 is a critical, unauthenticated remote code execution flaw in the F5 BIG-IP Traffic Management User Interface (TMUI), the appliance's web management console, rooted in a directory/path traversal issue (CWE-22) in undisclosed TMUI pages. It is triggered by sending crafted HTTP(S) requests to the management interface — classically path-traversal URLs beneath the TMUI application on the management port — which lets an attacker bypass authentication, read or delete arbitrary files, and execute commands without credentials. Successful exploitation yields full control of the BIG-IP system, which attackers can use to pivot into networks the appliance fronts, maintain persistence, and deploy ransomware. Any organization running an affected F5 BIG-IP appliance or virtual edition whose TMUI is reachable, or whose management network can be reached, is exposed; F5's installed base spans large enterprises and service providers, so the footprint is broad. Exploitation is confirmed in the wild: the flaw was mass-scanned and exploited within days of its July 2020 disclosure, it is listed in CISA KEV with known ransomware use, and EPSS assigns a ~100% probability of exploitation within 30 days.

Do: Patch immediately using F5's advisory K52145254 — upgrade BIG-IP to a fixed release per the vendor's version matrix, since CISA's required action is applying vendor updates. Until patched, restrict TMUI/management-interface access to trusted source IPs or a VPN (or disable TMUI if unused) and apply F5's published interim workaround. Because ransomware use is confirmed, hunt for indicators of compromise on both patched and unpatched appliances (unexpected files, webshells, modified login pages, new accounts or scheduled tasks) before treating systems as clean.