CVE-2026-98287

/// Technical 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

/// Remediation

Check the references section for vendor advisories, patches, and mitigation guidance. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

/// References