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Vulnerability record · CVE-2026-53003 · published 24 June 2026

CVE-2026-53003: Linux kernel vulnerability

Linux · Linux Kernel

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.

7.5 CVSS 3.1 High EPSS 0.72% · top 48.1%
7.5CVSS 3.1 base score
0.72%EPSS exploitation probability, 30 days
NoNot in CISA KEV
1Affected product versions listed by NVD
8References
14 Jul 2026Last modified by NVD

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.

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Affected products

1 vulnerable configurations from NVD's CPE data, grouped by vendor and product.

References

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

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Source: NIST National Vulnerability Database (record CVE-2026-53003), CISA KEV, FIRST EPSS (scores of 2026-09-26). This page is refreshed as NVD updates the record.