{"id":"CVE-2026-98158","title":"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 filt…","summary":"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 filt…","severity":"medium","cvss":5.5,"cvssVector":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H","cwe":["CWE-124"],"vendor":"Linux","product":"Linux","affected":["Linux >= 6722e78c90054101e6797d5944cdc81af9897a0a < 25f354c55b8435d1f51b8a0a05a3cfe429358523","Linux >= 6722e78c90054101e6797d5944cdc81af9897a0a < a86a17745c3e1c6fadd4d6e90c03552dfe531c8c","Linux >= 6722e78c90054101e6797d5944cdc81af9897a0a < ff035780adb0f49dc2c7ada26b4697849a68bec8","Linux >= 6722e78c90054101e6797d5944cdc81af9897a0a < c4bb894362d224b699e2f95c6c26707d9654e4a3","Linux >= 6722e78c90054101e6797d5944cdc81af9897a0a < d0fc3dabfe67caf084e7119ceb2ee23f5ad2f2da","Linux >= 6722e78c90054101e6797d5944cdc81af9897a0a < 0c53eb14975f029abd6b26896a460f0d2aaefe6b","Linux >= 6722e78c90054101e6797d5944cdc81af9897a0a < 717137221c7d90e7c98bda9a370c9da6cbf015e5","Linux >= 6722e78c90054101e6797d5944cdc81af9897a0a < 8dc5d98a16fa23c00999aecf10018c9f69fa5bf4","Linux 2.6.15"],"published":"2026-09-25","updated":"2026-10-03","sourceUpdated":"2026-10-03T11:18:37.947","source":"NVD","sourceUrl":"https://nvd.nist.gov/vuln/detail/CVE-2026-98158","references":[{"url":"https://git.kernel.org/stable/c/0c53eb14975f029abd6b26896a460f0d2aaefe6b","label":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://git.kernel.org/stable/c/25f354c55b8435d1f51b8a0a05a3cfe429358523","label":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://git.kernel.org/stable/c/717137221c7d90e7c98bda9a370c9da6cbf015e5","label":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://git.kernel.org/stable/c/8dc5d98a16fa23c00999aecf10018c9f69fa5bf4","label":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://git.kernel.org/stable/c/a86a17745c3e1c6fadd4d6e90c03552dfe531c8c","label":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://git.kernel.org/stable/c/c4bb894362d224b699e2f95c6c26707d9654e4a3","label":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://git.kernel.org/stable/c/d0fc3dabfe67caf084e7119ceb2ee23f5ad2f2da","label":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://git.kernel.org/stable/c/ff035780adb0f49dc2c7ada26b4697849a68bec8","label":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-98158.json"},{"url":"https://access.redhat.com/security/cve/CVE-2026-98158"},{"url":"https://bugzilla.redhat.com/show_bug.cgi?id=2541344"},{"url":"https://www.cve.org/CVERecord?id=CVE-2026-98158"},{"url":"https://nvd.nist.gov/vuln/detail/CVE-2026-98158"},{"url":"https://git.kernel.org/pub/scm/linux/security/vulns.git/plain/cve/published/2026/CVE-2026-98158.mbox"}],"tags":["nvd","cve.org","csaf","vex","red-hat"],"epss":0.00114,"epssPercentile":0.01485,"cvssSource":"vendor","ingestedAt":"2026-09-25T11:06:38.804Z","slug":"CVE-2026-98158","body":"## Overview\n\nIn 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.\n\n## Remediation\n\nRefer to the linked advisories for vendor-supplied fixes and affected version ranges.\n\n## Vendor advisories\n\n- **Red Hat VEX** · Moderate · affected: Red Hat Enterprise Linux 10, Red Hat Enterprise Linux 7, Red Hat Enterprise Linux 8, Red Hat Enterprise Linux 9, Red Hat OpenShift Container Platform 4 · no fix planned: Red Hat Enterprise Linux 10, Red Hat Enterprise Linux 7, Red Hat Enterprise Linux 8, Red Hat Enterprise Linux 9, … · updated 2026-10-17 · [vex](https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-98158.json)","depth":"sunlit","depthScore":30,"depthScoreParts":{"impact":30.3,"likelihood":0,"exploitation":0,"ransomware":0},"changes":[{"seq":212543,"id":"CVE-2026-98158","ts":1790668209455,"field":"cvss","old":null,"new":"5.5"},{"seq":212542,"id":"CVE-2026-98158","ts":1790668209455,"field":"severity","old":"none","new":"medium"}]}