LoFP LoFP / legitimate af_alg usage from unprivileged users is uncommon, but some kernel crypto tests, ipsec helpers, disk encryption tooling, hsm integrations, or approved security research systems may exercise this interface. verify the process, user, and host role before adding an exception.

Techniques

Sample rules

Potential Copy Fail (CVE-2026-31431) Exploitation via AF_ALG Socket

Description

Correlates a burst of non-root AF_ALG-class “socket”, “splice”, or “bound-socket” telemetry with a subsequent process execution where effective user is root but the login user remains non-root. This sequence matches common post-exploitation chains for Copy Fail (CVE-2026-31431) style abuse where AF_ALG and “splice” primitives precede executing a corrupted setuid binary from cache.

Detection logic

sequence with maxspan=60s
  [any where host.os.type == "linux" and    
   (
    (event.category == "process" and auditd.data.syscall == "socket" and auditd.data.a0 == "26") or 
    (event.category == "process" and auditd.data.syscall == "splice") or 
    (event.category == "network" and event.action == "bound-socket" and data_stream.dataset == "auditd_manager.auditd" and ?auditd.data.socket.family == "38") 
    )  
   and user.id != "0"]  by process.pid, host.id, user.id with runs=10
  [process where host.os.type == "linux"  and event.action == "executed" and 
   (
     (user.effective.id == "0" and user.id != "0") or 
     (process.name in ("bash", "sh", "zsh", "dash", "fish", "ksh", "busybox") and 
      process.args in ("-c", "--command", "-ic", "-ci", "-cl", "-lc", "-bash", "-sh", "-zsh", "-dash", "-fish", "-ksh"))
    )] by process.parent.pid, host.id, user.id