CVE-2026-49426 in FreeBSD
Summary
by MITRE • 08/19/2026
When auditing a system call executed via ptrace(PT_SC_REMOTE), the kernel passed the return value of an internal setup function to AUDIT_SYSCALL_EXIT() rather than the actual result of the executed system call. As a result, committed audit records for system calls which returned an error do not reflect the true outcome of the operation. That is, they indicate that the operation succeeded when it in fact failed.
Audit records for system calls executed via ptrace(PT_SC_REMOTE) may show an incorrect error status. An attacker with the ability to debug a process could use this to produce misleading audit trails, potentially undermining audit-based Intrusion Detection Systems (IDS).
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Analysis
by VulDB Data Team • 08/19/2026
The vulnerability described involves a critical flaw in the Linux kernel's auditing subsystem when handling system calls executed via ptrace using the PT_SC_REMOTE request. This specific mechanism allows one process to trace and execute system calls on behalf of another, often used for debugging or remote procedure call implementations within trusted environments. The core technical defect lies in how the return value is captured and logged during this operation. Instead of retrieving the actual result returned by the executed system call itself, the kernel incorrectly passes the return value from an internal setup function to the AUDIT_SYSCALL_EXIT macro. This misalignment means that the audit record generated for these specific remote-executed calls does not accurately reflect whether the underlying operation succeeded or failed.
This discrepancy creates a significant integrity issue within the auditing subsystem. When a system call executed via ptrace(PT_SC_REMOTE) encounters an error, such as permission denied or invalid argument, the kernel logs this event with a success status code rather than the appropriate negative errno value indicating failure. Consequently, security administrators and automated monitoring tools reviewing these audit trails will see records that indicate successful completion of operations that actually failed. This falsification of data undermines the fundamental purpose of system auditing, which is to provide an accurate and tamper-resistant record of system activity for forensic analysis and compliance verification.
The operational impact of this vulnerability extends beyond simple logging inaccuracies. It directly affects the reliability of audit-based Intrusion Detection Systems (IDS) and Security Information and Event Management (SIEM) platforms that rely on kernel audit logs to detect malicious behavior. An attacker with the ability to debug a target process, which typically requires specific privileges such as CAP_SYS_PTRACE or being part of the same user namespace, can exploit this flaw to produce misleading audit trails. By carefully crafting requests through ptrace(PT_SC_REMOTE), an adversary could execute unauthorized actions that fail but are logged as successes, thereby evading detection mechanisms that trigger on error codes or failure states. This capability allows for potential cover-up activities where malicious attempts are masked by false positive success logs, complicating incident response and forensic investigations.
From a classification perspective, this issue aligns with CWE-754: Improper Check for Unusual or Exceptional Conditions in the context of logging errors, but more specifically it falls under CWE-778: Insufficient Logging which leads to missed detection events due to incorrect status reporting. In terms of the MITRE ATT&CK framework, this vulnerability facilitates techniques related to Defense Evasion, particularly Log Manipulation and Indicator Removal on Hosts. The ability to alter the perceived outcome of system calls allows an attacker to manipulate the evidence trail, making it difficult for defenders to distinguish between legitimate activity and malicious attempts that were blocked but logged as successful.
Mitigation strategies must focus on correcting the kernel logic responsible for capturing return values in this specific ptrace context. Developers should ensure that AUDIT_SYSCALL_EXIT receives the actual system call result rather than intermediate setup function outputs when processing PT_SC_REMOTE requests. Until a patch is applied, administrators can mitigate risk by restricting access to ptrace capabilities through strict SELinux or AppArmor policies, ensuring that only highly trusted processes have debugging privileges. Additionally, implementing supplementary monitoring tools that cross-reference kernel audit logs with other system metrics, such as process state changes or file integrity monitors, may help detect discrepancies where logged success does not align with actual system behavior. Regular updates to the operating system and immediate application of vendor-provided security patches are essential to resolve this root cause in the auditing subsystem.