CVE-2026-89603
HighCVSS 8.4Exploitation Probability (EPSS)
Low risk4th percentile - higher than 4% of all known CVEs
Summary
In the Linux kernel, there is a race condition in seccomp handling after ptrace with TSYNC. If a thread is stopped in syscall_trace_enter() for ptrace, another thread can install a seccomp filter with SECCOMP_FILTER_FLAG_TSYNC, setting SYSCALL_WORK_SECCOMP on the stopped thread, but syscall_trace_enter() evaluates a cached 'work' variable and misses the new flag, silently bypassing the filter.
Risk Assessment
The race condition could allow an unprivileged process to execute a prohibited system call, such as execve, that the newly installed filter was intended to block. The risk of privilege escalation is high in multithreaded environments.
Recommendation
Update the Linux kernel to a version containing the fix that re-reads syscall_work flags after ptrace handling. Avoid relying solely on seccomp filters installed via TSYNC in ptrace scenarios until the fix is applied.
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Original NVD description (English source)
In the Linux kernel, the following vulnerability has been resolved: entry: Fix seccomp bypass after ptrace with TSYNC Sashiko review pointed out the following issue. If a thread is stopped in syscall_trace_enter() for ptrace, another thread can install a seccomp filter with SECCOMP_FILTER_FLAG_TSYNC (e.g., via seccomp_attach_filter()). This will successfully set SYSCALL_WORK_SECCOMP on the stopped thread, but syscall_trace_enter() evaluates a cached 'work' variable sampled on entry. Consequently, the subsequent check for SYSCALL_WORK_SECCOMP misses the newly assigned flag, and the filter is silently bypassed. This race condition could allow an unprivileged process to execute a prohibited system call (e.g., execve) that the newly installed filter was intended to block, especially since the tracer might have modified the system call number during the ptrace stop. Fix this by re-reading the syscall_work flags after ptrace handling, so that any new SYSCALL_WORK_SECCOMP flag set by another thread via TSYNC during the ptrace stop is observed before the subsequent seccomp check.
Vulnerability data from NVD (NIST) · CISA KEV · EPSS