CVE-2025-40281 in Linux
Summary
by MITRE • 12/07/2025
In the Linux kernel, the following vulnerability has been resolved:
sctp: prevent possible shift-out-of-bounds in sctp_transport_update_rto
syzbot reported a possible shift-out-of-bounds [1]
Blamed commit added rto_alpha_max and rto_beta_max set to 1000.
It is unclear if some sctp users are setting very large rto_alpha and/or rto_beta.
In order to prevent user regression, perform the test at run time.
Also add READ_ONCE() annotations as sysctl values can change under us.
[1]
UBSAN: shift-out-of-bounds in net/sctp/transport.c:509:41 shift exponent 64 is too large for 32-bit type 'unsigned int' CPU: 0 UID: 0 PID: 16704 Comm: syz.2.2320 Not tainted syzkaller #0 PREEMPT(full) Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/02/2025 Call Trace: <TASK> __dump_stack lib/dump_stack.c:94 [inline]
dump_stack_lvl+0x16c/0x1f0 lib/dump_stack.c:120 ubsan_epilogue lib/ubsan.c:233 [inline]
__ubsan_handle_shift_out_of_bounds+0x27f/0x420 lib/ubsan.c:494 sctp_transport_update_rto.cold+0x1c/0x34b net/sctp/transport.c:509 sctp_check_transmitted+0x11c4/0x1c30 net/sctp/outqueue.c:1502 sctp_outq_sack+0x4ef/0x1b20 net/sctp/outqueue.c:1338 sctp_cmd_process_sack net/sctp/sm_sideeffect.c:840 [inline]
sctp_cmd_interpreter net/sctp/sm_sideeffect.c:1372 [inline]
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Analysis
by VulDB Data Team • 02/23/2026
The vulnerability CVE-2025-40281 affects the Linux kernel's Stream Control Transmission Protocol implementation, specifically within the sctp_transport_update_rto function located in net/sctp/transport.c. This issue represents a potential shift-out-of-bounds condition that arises from improper handling of shift operations on 32-bit unsigned integer types. The flaw manifests when the system attempts to perform a bitwise left shift operation with an exponent that exceeds the bit width of the target data type, leading to undefined behavior and potential system instability. The vulnerability was identified through UBSAN (Undefined Behavior Sanitizer) reporting a shift-out-of-bounds error at line 509 of transport.c where the shift exponent 64 exceeds the 32-bit limit of unsigned int type. The root cause stems from changes introduced in a blamed commit that added rto_alpha_max and rto_beta_max parameters set to 1000, which can be manipulated by SCTP users to trigger the condition. This represents a classic example of improper input validation and arithmetic overflow handling that can be exploited to cause system crashes or potentially more serious security implications.
The technical implementation flaw occurs in the sctp_transport_update_rto function where runtime values from sysctl parameters are used in shift operations without proper bounds checking. The function processes RTO (Retransmission Timeout) values that control network retransmission behavior, but fails to validate that the shift exponents derived from user-configurable parameters remain within acceptable ranges for the target data types. The vulnerability is particularly concerning because it involves runtime sysctl values that can change during system operation, making the validation more complex. The addition of READ_ONCE() annotations addresses the race condition risk where sysctl values could be modified while the function executes, a pattern commonly addressed in kernel security contexts. This type of vulnerability falls under CWE-195: Signed to Unsigned Conversion Error and CWE-191: Integer Underflow or Wraparound, with potential ATT&CK techniques including privilege escalation through system instability and denial of service via kernel memory corruption.
The operational impact of this vulnerability extends beyond simple system crashes, as it can affect network reliability and availability in SCTP-based applications. When triggered, the shift-out-of-bounds condition can cause kernel panics or memory corruption that may result in complete system instability, particularly in environments heavily reliant on SCTP for communication. The vulnerability affects systems running Linux kernels with SCTP support, especially those that utilize user-configurable RTO parameters or have SCTP applications running with non-standard configurations. Network services relying on SCTP for signaling or data transmission could experience intermittent failures or complete outages when this condition is triggered. The issue is particularly relevant in telecommunications infrastructure, real-time communication systems, and any environment where SCTP is used for reliable data transfer. The potential for user-triggered exploitation means that malicious actors could deliberately configure SCTP parameters to cause system crashes, making this a significant concern for network service providers and system administrators managing critical infrastructure.
Mitigation strategies for CVE-2025-40281 should focus on implementing runtime validation of shift parameters and ensuring proper bounds checking before arithmetic operations. The fix involves adding runtime checks to validate that shift exponents derived from sysctl parameters do not exceed the bit width limitations of target data types, preventing the shift-out-of-bounds condition. System administrators should ensure they are running patched kernel versions that include the proper validation logic and READ_ONCE() annotations to prevent race conditions. Monitoring for abnormal SCTP parameter configurations and implementing proper input validation for network protocols can help detect potential exploitation attempts. The solution addresses the fundamental design flaw by preventing the problematic shift operations while maintaining backward compatibility with existing SCTP configurations. Security teams should also consider implementing network segmentation and monitoring to detect unusual SCTP behavior that might indicate exploitation attempts. Additionally, regular kernel updates and security assessments should be prioritized to address similar vulnerabilities in network protocol implementations, as this type of arithmetic overflow issue is common in kernel networking code and requires careful attention to integer handling and parameter validation.