In the Linux kernel, the following vulnerability has been resolved:
ppp_async: drop the errored frame instead of resetting its headroom
ppp_receive_nonmp_frame() prepends a two-byte direction tag before running
the pass/active BPF filters:
*(__be16 *)skb_push(skb, 2) = htons(PPP_FILTER_INBOUND_TAG);
Nothing on the receive path guarantees those two bytes of headroom. The
frame-error path in ppp_async's process_input_packet() resets a reused skb's
headroom to zero while claiming to restore it to a freshly allocated state -
but a fresh skb from dev_alloc_skb() carries NET_SKB_PAD:
err:
if (skb) {
/* make skb appear as freshly allocated */
skb_trim(skb, 0);
skb_reserve(skb, - skb_headroom(skb));
}
ap->rpkt still points at that skb, so the next frame is reassembled into it
with no headroom at all. A peer that sends a bad-FCS frame followed by one
beginning ff 03 then leaves a single byte of headroom by the time the filter
tag is pushed, which lands one byte below skb->head:
skbuff: skb_under_panic: len:49 put:2 head:ffff888003c10000
data:ffff888003c0ffff tail:0x30 end:0x640 dev:<NULL>
kernel BUG at net/core/skbuff.c:214!
RIP: 0010:skb_panic+0x13e/0x230
Call Trace:
skb_push+0xbd/0x100
ppp_receive_nonmp_frame+0x48a/0x1d10
ppp_input+0x4e9/0x2f80
ppp_async_process+0x2a/0xe0
tasklet_action_common+0x20f/0x8a0
handle_softirqs+0x18e/0x590
Kernel panic - not syncing: Fatal exception in interrupt
Zeroing the headroom violates the NET_SKB_PAD guarantee that dev_alloc_skb()
gives the rest of the receive path. Besides the filter panic above, when CCP
compression is enabled ppp_decompress_frame() hands skb->data - 2 to
->decompress()/->incomp(), which then reads out of bounds before skb->head
for the same reason.
Rather than restore the headroom, drop the errored frame - as ppp_synctty
already does on its error path - and clear ap->rpkt so the next frame is
reassembled into a fresh skb with proper headroom. This is simpler and fixes
both the filter under-panic and the CCP out-of-bounds read.
The original V1 of this patch made room in ppp_receive_nonmp_frame() with
skb_cow_head(); Eric pointed out that fixing the root cause in the transport
is the right approach.
Found by fuzzing the PPP receive path with a mutating peer on a pty; it is an
interesting (remote) DoS: root configures PPP, the peer supplies two crashing
frames. The reproducer (repro-ppp-skb.c, unchanged from v1) panics in about a
second, and returns cleanly with this applied.
References
Configurations
Configuration 1 (hide)
|
History
20 Oct 2026, 18:04
| Type | Values Removed | Values Added |
|---|---|---|
| CVSS |
v2 : v3 : |
v2 : unknown
v3 : 5.5 |
| CPE | cpe:2.3:o:linux:linux_kernel:7.3:rc1:*:*:*:*:*:* cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:* cpe:2.3:o:linux:linux_kernel:7.3:rc2:*:*:*:*:*:* |
|
| References | () https://git.kernel.org/stable/c/0c53eb14975f029abd6b26896a460f0d2aaefe6b - Patch | |
| References | () https://git.kernel.org/stable/c/25f354c55b8435d1f51b8a0a05a3cfe429358523 - Patch | |
| References | () https://git.kernel.org/stable/c/717137221c7d90e7c98bda9a370c9da6cbf015e5 - Patch | |
| References | () https://git.kernel.org/stable/c/8dc5d98a16fa23c00999aecf10018c9f69fa5bf4 - Patch | |
| References | () https://git.kernel.org/stable/c/a86a17745c3e1c6fadd4d6e90c03552dfe531c8c - Patch | |
| References | () https://git.kernel.org/stable/c/c4bb894362d224b699e2f95c6c26707d9654e4a3 - Patch | |
| References | () https://git.kernel.org/stable/c/d0fc3dabfe67caf084e7119ceb2ee23f5ad2f2da - Patch | |
| References | () https://git.kernel.org/stable/c/ff035780adb0f49dc2c7ada26b4697849a68bec8 - Patch | |
| CWE | CWE-125 | |
| First Time |
Linux linux Kernel
Linux |
03 Oct 2026, 11:18
| Type | Values Removed | Values Added |
|---|---|---|
| References |
|
25 Sep 2026, 11:17
| Type | Values Removed | Values Added |
|---|---|---|
| New CVE |
Information
Published : 2026-09-25 11:17
Updated : 2026-10-20 18:04
NVD link : CVE-2026-98158
Mitre link : CVE-2026-98158
CVE.ORG link : CVE-2026-98158
JSON object : View
Products Affected
linux
- linux_kernel
CWE
CWE-125
Out-of-bounds Read