CVE-2026-98158 (GCVE-0-2026-98158)
Vulnerability from cvelistv5 – Published: 2026-09-25 10:36 – Updated: 2026-10-19 09:14
VLAI
EPSS
VEX
Title
ppp_async: drop the errored frame instead of resetting its headroom
Summary
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.
Severity
5.5 (Medium)
Assigner
References
8 references
Impacted products
2 products
| Vendor | Product | Version | CPE status | |
|---|---|---|---|---|
| Linux | Linux |
Affected:
6722e78c90054101e6797d5944cdc81af9897a0a , < 25f354c55b8435d1f51b8a0a05a3cfe429358523
(git)
Affected: 6722e78c90054101e6797d5944cdc81af9897a0a , < a86a17745c3e1c6fadd4d6e90c03552dfe531c8c (git) Affected: 6722e78c90054101e6797d5944cdc81af9897a0a , < ff035780adb0f49dc2c7ada26b4697849a68bec8 (git) Affected: 6722e78c90054101e6797d5944cdc81af9897a0a , < c4bb894362d224b699e2f95c6c26707d9654e4a3 (git) Affected: 6722e78c90054101e6797d5944cdc81af9897a0a , < d0fc3dabfe67caf084e7119ceb2ee23f5ad2f2da (git) Affected: 6722e78c90054101e6797d5944cdc81af9897a0a , < 0c53eb14975f029abd6b26896a460f0d2aaefe6b (git) Affected: 6722e78c90054101e6797d5944cdc81af9897a0a , < 717137221c7d90e7c98bda9a370c9da6cbf015e5 (git) Affected: 6722e78c90054101e6797d5944cdc81af9897a0a , < 8dc5d98a16fa23c00999aecf10018c9f69fa5bf4 (git) |
guessed | |
| Linux | Linux |
Affected:
2.6.15
Unaffected: 0 , < 2.6.15 (semver) Unaffected: 5.10.271 , ≤ 5.10.* (semver) Unaffected: 5.15.222 , ≤ 5.15.* (semver) Unaffected: 6.1.189 , ≤ 6.1.* (semver) Unaffected: 6.6.158 , ≤ 6.6.* (semver) Unaffected: 6.12.111 , ≤ 6.12.* (semver) Unaffected: 6.18.53 , ≤ 6.18.* (semver) Unaffected: 7.2.7 , ≤ 7.2.* (semver) Unaffected: 7.3 , ≤ * (original_commit_for_fix) |
guessed |
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"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\u0027s process_input_packet() resets a reused skb\u0027s\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-\u003erpkt 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-\u003ehead:\n\n skbuff: skb_under_panic: len:49 put:2 head:ffff888003c10000\n data:ffff888003c0ffff tail:0x30 end:0x640 dev:\u003cNULL\u003e\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-\u003edata - 2 to\n-\u003edecompress()/-\u003eincomp(), which then reads out of bounds before skb-\u003ehead\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-\u003erpkt 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."
}
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{
"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\u0027s process_input_packet() resets a reused skb\u0027s\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-\u003erpkt 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-\u003ehead:\n\n skbuff: skb_under_panic: len:49 put:2 head:ffff888003c10000\n data:ffff888003c0ffff tail:0x30 end:0x640 dev:\u003cNULL\u003e\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-\u003edata - 2 to\n-\u003edecompress()/-\u003eincomp(), which then reads out of bounds before skb-\u003ehead\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-\u003erpkt 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."
}
],
"id": "CVE-2026-98158",
"lastModified": "2026-10-20T18:04:25.047",
"metrics": {
"cvssMetricV31": [
{
"cvssData": {
"attackComplexity": "LOW",
"attackVector": "LOCAL",
"availabilityImpact": "HIGH",
"baseScore": 5.5,
"baseSeverity": "MEDIUM",
"confidentialityImpact": "NONE",
"integrityImpact": "NONE",
"privilegesRequired": "LOW",
"scope": "UNCHANGED",
"userInteraction": "NONE",
"vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H",
"version": "3.1"
},
"exploitabilityScore": 1.8,
"impactScore": 3.6,
"source": "nvd@nist.gov",
"type": "Primary"
}
]
},
"published": "2026-09-25T11:17:47.510",
"references": [
{
"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"tags": [
"Patch"
],
"url": "https://git.kernel.org/stable/c/0c53eb14975f029abd6b26896a460f0d2aaefe6b"
},
{
"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"tags": [
"Patch"
],
"url": "https://git.kernel.org/stable/c/25f354c55b8435d1f51b8a0a05a3cfe429358523"
},
{
"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"tags": [
"Patch"
],
"url": "https://git.kernel.org/stable/c/717137221c7d90e7c98bda9a370c9da6cbf015e5"
},
{
"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"tags": [
"Patch"
],
"url": "https://git.kernel.org/stable/c/8dc5d98a16fa23c00999aecf10018c9f69fa5bf4"
},
{
"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"tags": [
"Patch"
],
"url": "https://git.kernel.org/stable/c/a86a17745c3e1c6fadd4d6e90c03552dfe531c8c"
},
{
"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"tags": [
"Patch"
],
"url": "https://git.kernel.org/stable/c/c4bb894362d224b699e2f95c6c26707d9654e4a3"
},
{
"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"tags": [
"Patch"
],
"url": "https://git.kernel.org/stable/c/d0fc3dabfe67caf084e7119ceb2ee23f5ad2f2da"
},
{
"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"tags": [
"Patch"
],
"url": "https://git.kernel.org/stable/c/ff035780adb0f49dc2c7ada26b4697849a68bec8"
}
],
"sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"vulnStatus": "Analyzed",
"weaknesses": [
{
"description": [
{
"lang": "en",
"value": "CWE-125"
}
],
"source": "nvd@nist.gov",
"type": "Primary"
}
]
}
},
"redhat_vex": {
"aggregate_severity": "Moderate",
"current_release_date": "2026-11-06T02:49:24+00:00",
"cve": "CVE-2026-98158",
"id": "CVE-2026-98158",
"initial_release_date": "2026-09-25T00:00:00+00:00",
"product_status:known_affected": "189",
"product_status:known_not_affected": "14",
"source": "Red Hat CSAF VEX",
"status": "final",
"title": "kernel: ppp_async: drop the errored frame instead of resetting its headroom",
"url": "https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-98158.json",
"version": "3"
}
}
}
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Drag nodes to arrange them. Double-click a related vulnerability to open it, or a source to visit its link. The Physics button on the left tunes the layout and the simulation; the legend at the bottom left hides or shows nodes by kind and by sighting type.
Experimental. This forecast is provided for visualization only and may change without notice. Do not use it for operational decisions.
Forecast uses a logistic model when the trend is rising, or an exponential decay model when the trend is falling. Fitted via linearized least squares.
Sightings
| Author | Source | Type | Date | Other |
|---|
Nomenclature
- Seen: The vulnerability was mentioned, discussed, or observed by the user.
- Confirmed: The vulnerability has been validated from an analyst's perspective.
- Published Proof of Concept: A public proof of concept is available for this vulnerability.
- Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
- Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
- Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
- Not confirmed: The user expressed doubt about the validity of the vulnerability.
- Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.
Vulnerability timeline
Sightings and recorded dates, grouped by day · UTC
How durations are calculated
Following the VTEM framework (Black Hat USA 2015), time to patch starts when the vendor or a coordinator was informed, total time to patch at discovery, and disclosure to patch at public disclosure; vendor response time runs from the report to its acknowledgement. Time to exploit and time unpatched start at the earliest discovery or report, falling back to public disclosure. Unpatched time ends at the first recorded patch, or the calculation time when no patch is recorded. Exploitation to patch shows the interval between those two events; a published proof of concept is a public exploit, not exploitation.
Each result shows its source dates. A negative interval means the end event came first; when date-only inputs leave the order open, the result says so. Date-only inputs are approximate. The earliest evidence wins: KEV report dates and sightings are labelled as such. Records describing another vulnerability are listed but never calculated from, and a PoC alone does not establish exploitation. Missing patch evidence does not prove that no patch exists. Filters below change the event list only.
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The MITRE ATT&CK techniques below are AI-generated suggestions, inferred from the description of the
vulnerability by the CIRCL/vulnerability-attack-technique-classification-roberta-base
model, served locally by ML-Gateway.
They have not been verified by an analyst and are provided for guidance only.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.
Browse all ATT&CK techniques and the vulnerabilities related to each.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.
Browse all ATT&CK techniques and the vulnerabilities related to each.
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Related by attack behaviour
Vulnerabilities whose description is nearest to this one in the vector space of the CIRCL/vulnerability-attack-technique-biencoder model. This is a similarity search over the bi-encoder space (plain cosine), not a classification, and it has no measured accuracy.