CVE-2026-98158
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:
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:
ap->rpkt still points at that skb, so the next frame is reassembled into it with no headroom at all.
Leer descripción completaMostrar menos
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:
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.
Detalles técnicos trazas, registros y código del informe original
*(__be16 *)skb_push(skb, 2) = htons(PPP_FILTER_INBOUND_TAG);
err:
if (skb) {
/* make skb appear as freshly allocated */
skb_trim(skb, 0);
skb_reserve(skb, - skb_headroom(skb));
}
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 interruptCVSS
NVD no ha asignado puntuación CVSS a esta CVE (habitual desde el cambio de política de abril de 2026).
Probabilidad de explotación (EPSS)
- Probabilidad de explotación en los próximos 30 días: 0.16%
- Percentil entre todas las CVEs puntuadas: 5
- Fecha de la puntuación: 6/10/2026
EPSS (Exploit Prediction Scoring System, de FIRST) estima la probabilidad de que una vulnerabilidad sea explotada en 30 días. Complementa a CVSS (impacto) y a CISA KEV (explotación confirmada).
Tecnologías afectadas (1)
⚠ Inferidas por IA a partir de la descripción — NVD aún no ha analizado esta CVE; no son CPE verificados.
Referencias
- https://git.kernel.org/stable/c/0c53eb14975f029abd6b26896a460f0d2aaefe6b
- https://git.kernel.org/stable/c/25f354c55b8435d1f51b8a0a05a3cfe429358523
- https://git.kernel.org/stable/c/717137221c7d90e7c98bda9a370c9da6cbf015e5
- https://git.kernel.org/stable/c/8dc5d98a16fa23c00999aecf10018c9f69fa5bf4
- https://git.kernel.org/stable/c/a86a17745c3e1c6fadd4d6e90c03552dfe531c8c
- https://git.kernel.org/stable/c/c4bb894362d224b699e2f95c6c26707d9654e4a3
- https://git.kernel.org/stable/c/d0fc3dabfe67caf084e7119ceb2ee23f5ad2f2da
- https://git.kernel.org/stable/c/ff035780adb0f49dc2c7ada26b4697849a68bec8
JSON original (NVD)
Mostrar
{
"id": "CVE-2026-98158",
"cveTags": [],
"metrics": {},
"affected": [
{
"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"affectedData": [
{
"repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
"vendor": "Linux",
"product": "Linux",
"versions": [
{
"status": "affected",
"version": "6722e78c90054101e6797d5944cdc81af9897a0a",
"lessThan": "25f354c55b8435d1f51b8a0a05a3cfe429358523",
"versionType": "git"
},
{
"status": "affected",
"version": "6722e78c90054101e6797d5944cdc81af9897a0a",
"lessThan": "a86a17745c3e1c6fadd4d6e90c03552dfe531c8c",
"versionType": "git"
},
{
"status": "affected",
"version": "6722e78c90054101e6797d5944cdc81af9897a0a",
"lessThan": "ff035780adb0f49dc2c7ada26b4697849a68bec8",
"versionType": "git"
},
{
"status": "affected",
"version": "6722e78c90054101e6797d5944cdc81af9897a0a",
"lessThan": "c4bb894362d224b699e2f95c6c26707d9654e4a3",
"versionType": "git"
},
{
"status": "affected",
"version": "6722e78c90054101e6797d5944cdc81af9897a0a",
"lessThan": "d0fc3dabfe67caf084e7119ceb2ee23f5ad2f2da",
"versionType": "git"
},
{
"status": "affected",
"version": "6722e78c90054101e6797d5944cdc81af9897a0a",
"lessThan": "0c53eb14975f029abd6b26896a460f0d2aaefe6b",
"versionType": "git"
},
{
"status": "affected",
"version": "6722e78c90054101e6797d5944cdc81af9897a0a",
"lessThan": "717137221c7d90e7c98bda9a370c9da6cbf015e5",
"versionType": "git"
},
{
"status": "affected",
"version": "6722e78c90054101e6797d5944cdc81af9897a0a",
"lessThan": "8dc5d98a16fa23c00999aecf10018c9f69fa5bf4",
"versionType": "git"
}
],
"programFiles": [
"drivers/net/ppp/ppp_async.c"
],
"defaultStatus": "unaffected"
},
{
"repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
"vendor": "Linux",
"product": "Linux",
"versions": [
{
"status": "affected",
"version": "2.6.15"
},
{
"status": "unaffected",
"version": "0",
"lessThan": "2.6.15",
"versionType": "semver"
},
{
"status": "unaffected",
"version": "5.10.271",
"versionType": "semver",
"lessThanOrEqual": "5.10.*"
},
{
"status": "unaffected",
"version": "5.15.222",
"versionType": "semver",
"lessThanOrEqual": "5.15.*"
},
{
"status": "unaffected",
"version": "6.1.189",
"versionType": "semver",
"lessThanOrEqual": "6.1.*"
},
{
"status": "unaffected",
"version": "6.6.158",
"versionType": "semver",
"lessThanOrEqual": "6.6.*"
},
{
"status": "unaffected",
"version": "6.12.111",
"versionType": "semver",
"lessThanOrEqual": "6.12.*"
},
{
"status": "unaffected",
"version": "6.18.53",
"versionType": "semver",
"lessThanOrEqual": "6.18.*"
},
{
"status": "unaffected",
"version": "7.2.7",
"versionType": "semver",
"lessThanOrEqual": "7.2.*"
},
{
"status": "unaffected",
"version": "7.3-rc3",
"versionType": "original_commit_for_fix",
"lessThanOrEqual": "*"
}
],
"programFiles": [
"drivers/net/ppp/ppp_async.c"
],
"defaultStatus": "affected"
}
]
}
],
"published": "2026-09-25T11:17:47.510",
"references": [
{
"url": "https://git.kernel.org/stable/c/0c53eb14975f029abd6b26896a460f0d2aaefe6b",
"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
},
{
"url": "https://git.kernel.org/stable/c/25f354c55b8435d1f51b8a0a05a3cfe429358523",
"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
},
{
"url": "https://git.kernel.org/stable/c/717137221c7d90e7c98bda9a370c9da6cbf015e5",
"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
},
{
"url": "https://git.kernel.org/stable/c/8dc5d98a16fa23c00999aecf10018c9f69fa5bf4",
"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
},
{
"url": "https://git.kernel.org/stable/c/a86a17745c3e1c6fadd4d6e90c03552dfe531c8c",
"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
},
{
"url": "https://git.kernel.org/stable/c/c4bb894362d224b699e2f95c6c26707d9654e4a3",
"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
},
{
"url": "https://git.kernel.org/stable/c/d0fc3dabfe67caf084e7119ceb2ee23f5ad2f2da",
"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
},
{
"url": "https://git.kernel.org/stable/c/ff035780adb0f49dc2c7ada26b4697849a68bec8",
"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
}
],
"vulnStatus": "Undergoing Analysis",
"descriptions": [
{
"lang": "en",
"value": "In the Linux kernel, the following vulnerability has been resolved:\n\nppp_async: drop the errored frame instead of resetting its headroom\n\nppp_receive_nonmp_frame() prepends a two-byte direction tag before running\nthe pass/active BPF filters:\n\n\t*(__be16 *)skb_push(skb, 2) = htons(PPP_FILTER_INBOUND_TAG);\n\nNothing on the receive path guarantees those two bytes of headroom. The\nframe-error path in ppp_async's process_input_packet() resets a reused skb's\nheadroom to zero while claiming to restore it to a freshly allocated state -\nbut a fresh skb from dev_alloc_skb() carries NET_SKB_PAD:\n\n\terr:\n\t\tif (skb) {\n\t\t\t/* make skb appear as freshly allocated */\n\t\t\tskb_trim(skb, 0);\n\t\t\tskb_reserve(skb, - skb_headroom(skb));\n\t\t}\n\nap->rpkt still points at that skb, so the next frame is reassembled into it\nwith no headroom at all. A peer that sends a bad-FCS frame followed by one\nbeginning ff 03 then leaves a single byte of headroom by the time the filter\ntag is pushed, which lands one byte below skb->head:\n\n skbuff: skb_under_panic: len:49 put:2 head:ffff888003c10000\n data:ffff888003c0ffff tail:0x30 end:0x640 dev:<NULL>\n kernel BUG at net/core/skbuff.c:214!\n RIP: 0010:skb_panic+0x13e/0x230\n Call Trace:\n skb_push+0xbd/0x100\n ppp_receive_nonmp_frame+0x48a/0x1d10\n ppp_input+0x4e9/0x2f80\n ppp_async_process+0x2a/0xe0\n tasklet_action_common+0x20f/0x8a0\n handle_softirqs+0x18e/0x590\n Kernel panic - not syncing: Fatal exception in interrupt\n\nZeroing the headroom violates the NET_SKB_PAD guarantee that dev_alloc_skb()\ngives the rest of the receive path. Besides the filter panic above, when CCP\ncompression is enabled ppp_decompress_frame() hands skb->data - 2 to\n->decompress()/->incomp(), which then reads out of bounds before skb->head\nfor the same reason.\n\nRather than restore the headroom, drop the errored frame - as ppp_synctty\nalready does on its error path - and clear ap->rpkt so the next frame is\nreassembled into a fresh skb with proper headroom. This is simpler and fixes\nboth the filter under-panic and the CCP out-of-bounds read.\n\nThe original V1 of this patch made room in ppp_receive_nonmp_frame() with\nskb_cow_head(); Eric pointed out that fixing the root cause in the transport\nis the right approach.\n\nFound by fuzzing the PPP receive path with a mutating peer on a pty; it is an\ninteresting (remote) DoS: root configures PPP, the peer supplies two crashing\nframes. The reproducer (repro-ppp-skb.c, unchanged from v1) panics in about a\nsecond, and returns cleanly with this applied."
}
],
"lastModified": "2026-10-03T11:18:37.947",
"sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
}