Datadog Builds Agent-Assisted Detection for Linux Copy Fail Vulnerability
Summary
Datadog details behavioral detections for CVE-2026-31431, a Linux kernel flaw that lets unprivileged users corrupt file page caches and potentially gain root access, and describes using coding agents to build and test detection rules.
Key points
- CVE-2026-31431 affects a broad range of Linux kernel versions and has been added to CISA’s Known Exploited Vulnerabilities catalog; active exploitation is confirmed, according to the article.
- The exploit uses unprivileged AF_ALG sockets and splice() to corrupt cached file contents without writing to disk or changing file metadata.
- Datadog’s detection chain tracks an unprivileged process binding an AF_ALG socket, configuring it with SOL_ALG, then splicing a SUID file or opening sensitive system files.
- The article describes using coding agents to analyze exploit behavior, prototype and test rules, identify detection gaps, and package the resulting content pack.
- The content pack requires Datadog Agent v7.68 or later; the article also provides a Cloud SIEM query and a method to identify affected kernels.
- Datadog recommends patching affected kernels, disabling algif_aead where patching is delayed, enabling the detection pack, and hunting for prior exploitation.
Article Details
- Defense Focus
- Detect and hunt exploitation of CVE-2026-31431 (Copy Fail), scope affected Linux hosts and containers, and reduce exposure until kernels are patched.
- Detection Methods
- Use a process-scoped, three-stage behavioral chain: an unprivileged process binds an AF_ALG socket, calls setsockopt with SOL_ALG, then splices a SUID file or opens a sensitive system file read-only.
- Use a generic S_ISUID file-mode check rather than a hardcoded list of setuid binaries.
- Apply a cooldown to limit repeated signals from the exploit's rapid splice operations.
- Hunt for algif_aead kernel module loads as a possible indicator of exploitation preparation, especially on systems without a normal kernel-cryptography use case.
- Use kernel-version exposure assessment to identify hosts and containers running affected versions.
- Data Sources
- Kernel bind, setsockopt, splice, and open events, including process effective UID, socket family, setsockopt level, file mode, file path, and open flags.
- Auditd or forwarded syslog records for algif_aead module loads.
- Kernel version and vulnerability advisory status for hosts and containers.
- Rule Types
- Chained behavioral detection with process-scoped state and time-to-live.
- File-mode and path-based syscall detections.
- Log Management search query for kernel module-load evidence.
- Vulnerability inventory query filtering by CVE and status.
- Platforms
- Linux
- Defensive Actions
- Prioritize patching affected kernels; the article identifies this as the only complete mitigation.
- Disable algif_aead on systems that cannot be patched immediately.
- Enable the CVE-2026-31431 Copy Fail Exploit content pack; it requires Datadog Agent v7.68 or greater.
- Restrict AF_ALG socket creation with updated AppArmor, SELinux, or SecComp profiles where appropriate.
- Use Cloud SIEM to hunt retrospectively for exploitation attempts and CSM Vulnerabilities to audit affected hosts and containers.
CVE
Vendors
Products
AppArmorRestricting socket creation through updated AppArmor, SELinux, or SecComp profiles can effectively shrink the attack surface of a compromised container.Cloud SIEMHunting for exploitation with Cloud SIEMCSM VulnerabilitiesScoping exposure with CSM VulnerabilitiesDatadog AgentThe rules require Datadog Agent v7.68 or greater.Datadog Workload ProtectionDetecting CVE-2026-31431 with Datadog Workload ProtectionSecCompRestricting socket creation through updated AppArmor, SELinux, or SecComp profiles can effectively shrink the attack surface of a compromised container.SELinuxRestricting socket creation through updated AppArmor, SELinux, or SecComp profiles can effectively shrink the attack surface of a compromised container.