CVE-2025-68188 in Linux
Summary
by MITRE • 12/16/2025
In the Linux kernel, the following vulnerability has been resolved:
tcp: use dst_dev_rcu() in tcp_fastopen_active_disable_ofo_check()
Use RCU to avoid a pair of atomic operations and a potential UAF on dst_dev()->flags.
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Analysis
by VulDB Data Team • 02/21/2026
The vulnerability identified as CVE-2025-68188 resides within the Linux kernel's Transmission Control Protocol implementation, specifically affecting the tcp_fastopen_active_disable_ofo_check() function. This issue represents a subtle but critical race condition that could potentially lead to a use-after-free condition, making it particularly dangerous in network-intensive environments where TCP Fast Open functionality is actively utilized.
The technical flaw manifests in how the kernel handles device reference counting during TCP Fast Open operations. The original implementation employed atomic operations to manage access to the destination device flags, creating a potential race condition scenario where concurrent access could result in improper memory management. The fix addresses this by transitioning to RCU (Read-Copy-Update) mechanisms, which provide a more robust approach to handling concurrent access patterns without the overhead of atomic operations. This change specifically targets the dst_dev_rcu() function, which provides a read-only reference to device information under RCU protection, eliminating the potential for use-after-free conditions that could occur when accessing dst_dev()->flags directly.
The operational impact of this vulnerability extends beyond simple memory corruption, as it could potentially be exploited to achieve privilege escalation or system instability. Network servers and high-throughput applications that rely heavily on TCP Fast Open functionality are particularly at risk, since this vulnerability specifically affects the active TCP Fast Open disable mechanism. The use-after-free condition could allow an attacker to manipulate memory contents or potentially execute arbitrary code with kernel privileges, depending on the specific exploitation scenario and system configuration. Systems running with TCP Fast Open enabled and experiencing high concurrent connection loads would be most vulnerable to exploitation attempts.
Mitigation strategies for this vulnerability primarily involve updating to the patched kernel version that implements the RCU-based solution. Organizations should prioritize patch management for all systems running affected kernel versions, particularly those hosting network services that utilize TCP Fast Open. Network administrators should monitor for any unusual system behavior or performance degradation that might indicate exploitation attempts. The fix demonstrates adherence to security best practices by implementing proper concurrency control mechanisms rather than relying on atomic operations for reference counting scenarios. This approach aligns with CWE-362, which addresses race conditions in concurrent programming, and follows ATT&CK techniques related to privilege escalation through kernel vulnerabilities. The implementation of RCU mechanisms also reflects modern kernel security practices for managing shared data structures in high-concurrency environments.