{"id":"CVE-2026-98158","state":"PUBLISHED","title":"ppp_async: drop the errored frame instead of resetting its headroom","description":"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.","publishedAt":"2026-09-25T10:36:27.608Z","updatedAt":"2026-10-19T09:14:52.068Z","severity":null,"assigner":"Linux","products":["Linux Linux"],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"6722e78c90054101e6797d5944cdc81af9897a0a","status":"affected","lessThan":"25f354c55b8435d1f51b8a0a05a3cfe429358523","versionType":"git"},{"version":"6722e78c90054101e6797d5944cdc81af9897a0a","status":"affected","lessThan":"a86a17745c3e1c6fadd4d6e90c03552dfe531c8c","versionType":"git"},{"version":"6722e78c90054101e6797d5944cdc81af9897a0a","status":"affected","lessThan":"ff035780adb0f49dc2c7ada26b4697849a68bec8","versionType":"git"},{"version":"6722e78c90054101e6797d5944cdc81af9897a0a","status":"affected","lessThan":"c4bb894362d224b699e2f95c6c26707d9654e4a3","versionType":"git"},{"version":"6722e78c90054101e6797d5944cdc81af9897a0a","status":"affected","lessThan":"d0fc3dabfe67caf084e7119ceb2ee23f5ad2f2da","versionType":"git"},{"version":"6722e78c90054101e6797d5944cdc81af9897a0a","status":"affected","lessThan":"0c53eb14975f029abd6b26896a460f0d2aaefe6b","versionType":"git"},{"version":"6722e78c90054101e6797d5944cdc81af9897a0a","status":"affected","lessThan":"717137221c7d90e7c98bda9a370c9da6cbf015e5","versionType":"git"},{"version":"6722e78c90054101e6797d5944cdc81af9897a0a","status":"affected","lessThan":"8dc5d98a16fa23c00999aecf10018c9f69fa5bf4","versionType":"git"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["drivers/net/ppp/ppp_async.c"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"2.6.15","status":"affected"},{"version":"0","status":"unaffected","lessThan":"2.6.15","versionType":"semver"},{"version":"5.10.271","status":"unaffected","lessThanOrEqual":"5.10.*","versionType":"semver"},{"version":"5.15.222","status":"unaffected","lessThanOrEqual":"5.15.*","versionType":"semver"},{"version":"6.1.189","status":"unaffected","lessThanOrEqual":"6.1.*","versionType":"semver"},{"version":"6.6.158","status":"unaffected","lessThanOrEqual":"6.6.*","versionType":"semver"},{"version":"6.12.111","status":"unaffected","lessThanOrEqual":"6.12.*","versionType":"semver"},{"version":"6.18.53","status":"unaffected","lessThanOrEqual":"6.18.*","versionType":"semver"},{"version":"7.2.7","status":"unaffected","lessThanOrEqual":"7.2.*","versionType":"semver"},{"version":"7.3","status":"unaffected","lessThanOrEqual":"*","versionType":"original_commit_for_fix"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["drivers/net/ppp/ppp_async.c"]}],"references":["https://git.kernel.org/stable/c/25f354c55b8435d1f51b8a0a05a3cfe429358523","https://git.kernel.org/stable/c/a86a17745c3e1c6fadd4d6e90c03552dfe531c8c","https://git.kernel.org/stable/c/ff035780adb0f49dc2c7ada26b4697849a68bec8","https://git.kernel.org/stable/c/c4bb894362d224b699e2f95c6c26707d9654e4a3","https://git.kernel.org/stable/c/d0fc3dabfe67caf084e7119ceb2ee23f5ad2f2da","https://git.kernel.org/stable/c/0c53eb14975f029abd6b26896a460f0d2aaefe6b","https://git.kernel.org/stable/c/717137221c7d90e7c98bda9a370c9da6cbf015e5","https://git.kernel.org/stable/c/8dc5d98a16fa23c00999aecf10018c9f69fa5bf4"],"weaknesses":[],"ingestedAt":"2026-10-29T20:13:43.249Z","source":{"repository":"CVEProject/cvelistV5","path":"cves/2026/98xxx/CVE-2026-98158.json","commit":"556c9d3a8cd17e218bb8e452ba7cd619a384ff47"},"raw":{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2026-98158","state":"PUBLISHED","datePublished":"2026-09-25T10:36:27.608Z","dateUpdated":"2026-10-19T09:14:52.068Z","assignerShortName":"Linux","assignerOrgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateReserved":"2026-09-25T10:25:14.321Z"},"containers":{"cna":{"title":"ppp_async: drop the errored frame instead of resetting its headroom","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."}],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"6722e78c90054101e6797d5944cdc81af9897a0a","status":"affected","lessThan":"25f354c55b8435d1f51b8a0a05a3cfe429358523","versionType":"git"},{"version":"6722e78c90054101e6797d5944cdc81af9897a0a","status":"affected","lessThan":"a86a17745c3e1c6fadd4d6e90c03552dfe531c8c","versionType":"git"},{"version":"6722e78c90054101e6797d5944cdc81af9897a0a","status":"affected","lessThan":"ff035780adb0f49dc2c7ada26b4697849a68bec8","versionType":"git"},{"version":"6722e78c90054101e6797d5944cdc81af9897a0a","status":"affected","lessThan":"c4bb894362d224b699e2f95c6c26707d9654e4a3","versionType":"git"},{"version":"6722e78c90054101e6797d5944cdc81af9897a0a","status":"affected","lessThan":"d0fc3dabfe67caf084e7119ceb2ee23f5ad2f2da","versionType":"git"},{"version":"6722e78c90054101e6797d5944cdc81af9897a0a","status":"affected","lessThan":"0c53eb14975f029abd6b26896a460f0d2aaefe6b","versionType":"git"},{"version":"6722e78c90054101e6797d5944cdc81af9897a0a","status":"affected","lessThan":"717137221c7d90e7c98bda9a370c9da6cbf015e5","versionType":"git"},{"version":"6722e78c90054101e6797d5944cdc81af9897a0a","status":"affected","lessThan":"8dc5d98a16fa23c00999aecf10018c9f69fa5bf4","versionType":"git"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["drivers/net/ppp/ppp_async.c"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"2.6.15","status":"affected"},{"version":"0","status":"unaffected","lessThan":"2.6.15","versionType":"semver"},{"version":"5.10.271","status":"unaffected","lessThanOrEqual":"5.10.*","versionType":"semver"},{"version":"5.15.222","status":"unaffected","lessThanOrEqual":"5.15.*","versionType":"semver"},{"version":"6.1.189","status":"unaffected","lessThanOrEqual":"6.1.*","versionType":"semver"},{"version":"6.6.158","status":"unaffected","lessThanOrEqual":"6.6.*","versionType":"semver"},{"version":"6.12.111","status":"unaffected","lessThanOrEqual":"6.12.*","versionType":"semver"},{"version":"6.18.53","status":"unaffected","lessThanOrEqual":"6.18.*","versionType":"semver"},{"version":"7.2.7","status":"unaffected","lessThanOrEqual":"7.2.*","versionType":"semver"},{"version":"7.3","status":"unaffected","lessThanOrEqual":"*","versionType":"original_commit_for_fix"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["drivers/net/ppp/ppp_async.c"]}],"references":[{"url":"https://git.kernel.org/stable/c/25f354c55b8435d1f51b8a0a05a3cfe429358523"},{"url":"https://git.kernel.org/stable/c/a86a17745c3e1c6fadd4d6e90c03552dfe531c8c"},{"url":"https://git.kernel.org/stable/c/ff035780adb0f49dc2c7ada26b4697849a68bec8"},{"url":"https://git.kernel.org/stable/c/c4bb894362d224b699e2f95c6c26707d9654e4a3"},{"url":"https://git.kernel.org/stable/c/d0fc3dabfe67caf084e7119ceb2ee23f5ad2f2da"},{"url":"https://git.kernel.org/stable/c/0c53eb14975f029abd6b26896a460f0d2aaefe6b"},{"url":"https://git.kernel.org/stable/c/717137221c7d90e7c98bda9a370c9da6cbf015e5"},{"url":"https://git.kernel.org/stable/c/8dc5d98a16fa23c00999aecf10018c9f69fa5bf4"}],"providerMetadata":{"shortName":"Linux","orgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateUpdated":"2026-10-19T09:14:52.068Z"},"cpeApplicability":[{"nodes":[{"operator":"OR","negate":false,"cpeMatch":[{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"2.6.15","versionEndExcluding":"5.10.271"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"2.6.15","versionEndExcluding":"5.15.222"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"2.6.15","versionEndExcluding":"6.1.189"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"2.6.15","versionEndExcluding":"6.6.158"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"2.6.15","versionEndExcluding":"6.12.111"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"2.6.15","versionEndExcluding":"6.18.53"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"2.6.15","versionEndExcluding":"7.2.7"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"2.6.15","versionEndExcluding":"7.3"}]}]}],"x_generator":{"engine":"bippy-1.2.0"}}}}}