{"id":"CVE-2025-39673","state":"PUBLISHED","title":"ppp: fix race conditions in ppp_fill_forward_path","description":"In the Linux kernel, the following vulnerability has been resolved:\n\nppp: fix race conditions in ppp_fill_forward_path\n\nppp_fill_forward_path() has two race conditions:\n\n1. The ppp->channels list can change between list_empty() and\n   list_first_entry(), as ppp_lock() is not held. If the only channel\n   is deleted in ppp_disconnect_channel(), list_first_entry() may\n   access an empty head or a freed entry, and trigger a panic.\n\n2. pch->chan can be NULL. When ppp_unregister_channel() is called,\n   pch->chan is set to NULL before pch is removed from ppp->channels.\n\nFix these by using a lockless RCU approach:\n- Use list_first_or_null_rcu() to safely test and access the first list\n  entry.\n- Convert list modifications on ppp->channels to their RCU variants and\n  add synchronize_net() after removal.\n- Check for a NULL pch->chan before dereferencing it.","publishedAt":"2025-09-05T17:20:38.769Z","updatedAt":"2026-10-15T22:02:29.786Z","severity":{"score":9.8,"label":"Critical","version":"3.1","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H","source":"Linux"},"assigner":"Linux","products":["Linux Linux"],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"f6efc675c9dd8d93f826b79ae7e33e03301db609","status":"affected","lessThan":"9a1969fbffc1f1900d92d7594b1b7d8d72ef3dc7","versionType":"git"},{"version":"f6efc675c9dd8d93f826b79ae7e33e03301db609","status":"affected","lessThan":"0f1630be6fcca3f0c63e4b242ad202e5cde28a40","versionType":"git"},{"version":"f6efc675c9dd8d93f826b79ae7e33e03301db609","status":"affected","lessThan":"ca18d751bcc9faf5b7e82e9fae1223d103928181","versionType":"git"},{"version":"f6efc675c9dd8d93f826b79ae7e33e03301db609","status":"affected","lessThan":"94731cc551e29511d85aa8dec61a6c071b1f2430","versionType":"git"},{"version":"f6efc675c9dd8d93f826b79ae7e33e03301db609","status":"affected","lessThan":"f97f6475fdcb3c28ff3c55cc4b7bde632119ec08","versionType":"git"},{"version":"f6efc675c9dd8d93f826b79ae7e33e03301db609","status":"affected","lessThan":"0417adf367a0af11adf7ace849af4638cfb573f7","versionType":"git"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["drivers/net/ppp/ppp_generic.c"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"5.13","status":"affected"},{"version":"0","status":"unaffected","lessThan":"5.13","versionType":"semver"},{"version":"5.15.190","status":"unaffected","lessThanOrEqual":"5.15.*","versionType":"semver"},{"version":"6.1.149","status":"unaffected","lessThanOrEqual":"6.1.*","versionType":"semver"},{"version":"6.6.103","status":"unaffected","lessThanOrEqual":"6.6.*","versionType":"semver"},{"version":"6.12.44","status":"unaffected","lessThanOrEqual":"6.12.*","versionType":"semver"},{"version":"6.16.4","status":"unaffected","lessThanOrEqual":"6.16.*","versionType":"semver"},{"version":"6.17","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_generic.c"]}],"references":["https://git.kernel.org/stable/c/9a1969fbffc1f1900d92d7594b1b7d8d72ef3dc7","https://git.kernel.org/stable/c/0f1630be6fcca3f0c63e4b242ad202e5cde28a40","https://git.kernel.org/stable/c/ca18d751bcc9faf5b7e82e9fae1223d103928181","https://git.kernel.org/stable/c/94731cc551e29511d85aa8dec61a6c071b1f2430","https://git.kernel.org/stable/c/f97f6475fdcb3c28ff3c55cc4b7bde632119ec08","https://git.kernel.org/stable/c/0417adf367a0af11adf7ace849af4638cfb573f7","https://lists.debian.org/debian-lts-announce/2025/10/msg00008.html","https://cert-portal.siemens.com/productcert/html/ssa-032379.html"],"weaknesses":[],"ingestedAt":"2026-10-29T20:09:09.358Z","source":{"repository":"CVEProject/cvelistV5","path":"cves/2025/39xxx/CVE-2025-39673.json","commit":"556c9d3a8cd17e218bb8e452ba7cd619a384ff47"},"raw":{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2025-39673","state":"PUBLISHED","datePublished":"2025-09-05T17:20:38.769Z","dateUpdated":"2026-10-15T22:02:29.786Z","assignerShortName":"Linux","assignerOrgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateReserved":"2025-04-16T07:20:57.112Z"},"containers":{"cna":{"title":"ppp: fix race conditions in ppp_fill_forward_path","descriptions":[{"lang":"en","value":"In the Linux kernel, the following vulnerability has been resolved:\n\nppp: fix race conditions in ppp_fill_forward_path\n\nppp_fill_forward_path() has two race conditions:\n\n1. The ppp->channels list can change between list_empty() and\n   list_first_entry(), as ppp_lock() is not held. If the only channel\n   is deleted in ppp_disconnect_channel(), list_first_entry() may\n   access an empty head or a freed entry, and trigger a panic.\n\n2. pch->chan can be NULL. When ppp_unregister_channel() is called,\n   pch->chan is set to NULL before pch is removed from ppp->channels.\n\nFix these by using a lockless RCU approach:\n- Use list_first_or_null_rcu() to safely test and access the first list\n  entry.\n- Convert list modifications on ppp->channels to their RCU variants and\n  add synchronize_net() after removal.\n- Check for a NULL pch->chan before dereferencing it."}],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"f6efc675c9dd8d93f826b79ae7e33e03301db609","status":"affected","lessThan":"9a1969fbffc1f1900d92d7594b1b7d8d72ef3dc7","versionType":"git"},{"version":"f6efc675c9dd8d93f826b79ae7e33e03301db609","status":"affected","lessThan":"0f1630be6fcca3f0c63e4b242ad202e5cde28a40","versionType":"git"},{"version":"f6efc675c9dd8d93f826b79ae7e33e03301db609","status":"affected","lessThan":"ca18d751bcc9faf5b7e82e9fae1223d103928181","versionType":"git"},{"version":"f6efc675c9dd8d93f826b79ae7e33e03301db609","status":"affected","lessThan":"94731cc551e29511d85aa8dec61a6c071b1f2430","versionType":"git"},{"version":"f6efc675c9dd8d93f826b79ae7e33e03301db609","status":"affected","lessThan":"f97f6475fdcb3c28ff3c55cc4b7bde632119ec08","versionType":"git"},{"version":"f6efc675c9dd8d93f826b79ae7e33e03301db609","status":"affected","lessThan":"0417adf367a0af11adf7ace849af4638cfb573f7","versionType":"git"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["drivers/net/ppp/ppp_generic.c"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"5.13","status":"affected"},{"version":"0","status":"unaffected","lessThan":"5.13","versionType":"semver"},{"version":"5.15.190","status":"unaffected","lessThanOrEqual":"5.15.*","versionType":"semver"},{"version":"6.1.149","status":"unaffected","lessThanOrEqual":"6.1.*","versionType":"semver"},{"version":"6.6.103","status":"unaffected","lessThanOrEqual":"6.6.*","versionType":"semver"},{"version":"6.12.44","status":"unaffected","lessThanOrEqual":"6.12.*","versionType":"semver"},{"version":"6.16.4","status":"unaffected","lessThanOrEqual":"6.16.*","versionType":"semver"},{"version":"6.17","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_generic.c"]}],"references":[{"url":"https://git.kernel.org/stable/c/9a1969fbffc1f1900d92d7594b1b7d8d72ef3dc7"},{"url":"https://git.kernel.org/stable/c/0f1630be6fcca3f0c63e4b242ad202e5cde28a40"},{"url":"https://git.kernel.org/stable/c/ca18d751bcc9faf5b7e82e9fae1223d103928181"},{"url":"https://git.kernel.org/stable/c/94731cc551e29511d85aa8dec61a6c071b1f2430"},{"url":"https://git.kernel.org/stable/c/f97f6475fdcb3c28ff3c55cc4b7bde632119ec08"},{"url":"https://git.kernel.org/stable/c/0417adf367a0af11adf7ace849af4638cfb573f7"}],"metrics":[{"cvssV3_1":{"version":"3.1","vectorString":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H","baseScore":9.8,"baseSeverity":"CRITICAL"},"scenarios":[{"lang":"en","value":"AV:N - The race's teardown side is reachable from received packets — an unauthenticated spoofed PPPoE PADT frame drives `pppoe_disc_rcv()` → `ppp_unregister_channel()`, and remote L2TP/PPTP peers drive the same teardown over routed IP — while the reader side is triggered by ordinary forwarded traffic entering the nftables flowtable/HW-offload path from any remote host.\nAC:L - The attacker controls both sides of the race and can retry indefinitely: repeated session teardowns concurrently with a stream of new forwarded connections that each invoke `ppp_fill_forward_path()`, on a widely deployed default configuration (PPPoE/L2TP WAN plus flow offload).\nPR:N - PADT injection requires no credentials whatsoever (`pppoe_disc_rcv()` matches only session-id and source MAC, both observable), and generating forwarded traffic requires none; even the local variant only needs CAP_NET_ADMIN, which is obtainable unprivileged via user namespaces.\nUI:N - No victim action is needed — the attacker supplies both the teardown trigger and the forwarded traffic; PPP session teardown on remote protocol messages is automatic daemon behaviour, not user interaction.\nS:U - The corruption and its consequences are confined to the kernel's own security authority; no VM, IOMMU, or sandbox boundary is crossed.\nC:H - The commit states `list_first_entry()` may return \"a freed entry\", giving a use-after-free read of a `struct channel` slab object, and the empty-head case yields an unbounded wild-pointer read through `chan->ops`, both usable to disclose arbitrary kernel memory.\nI:H - The UAF terminates in an indirect call through `chan->ops->fill_forward_path`, so an attacker who reclaims the freed `struct channel` allocation with sprayed data controls the function pointer, yielding control-flow hijack rather than a mere read.\nA:H - The commit explicitly says the list race will \"trigger a panic\", and the second race is an outright NULL dereference on `chan->ops` — either way a remotely reproducible kernel oops on a router in the forwarding fast path."}]}],"providerMetadata":{"shortName":"Linux","orgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateUpdated":"2026-08-05T12:04:28.071Z"},"cpeApplicability":[{"nodes":[{"operator":"OR","negate":false,"cpeMatch":[{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"5.13","versionEndExcluding":"5.15.190"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"5.13","versionEndExcluding":"6.1.149"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"5.13","versionEndExcluding":"6.6.103"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"5.13","versionEndExcluding":"6.12.44"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"5.13","versionEndExcluding":"6.16.4"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"5.13","versionEndExcluding":"6.17"}]}]}],"x_generator":{"engine":"bippy-1.2.0"}},"adp":[{"title":"CVE Program Container","references":[{"url":"https://lists.debian.org/debian-lts-announce/2025/10/msg00008.html"}],"providerMetadata":{"shortName":"CVE","orgId":"af854a3a-2127-422b-91ae-364da2661108","dateUpdated":"2025-11-03T17:42:08.016Z"}},{"affected":[{"vendor":"Siemens","product":"SIMATIC CN 4100","defaultStatus":"unknown","versions":[{"version":"0","status":"affected","lessThan":"V5.0","versionType":"custom"}]}],"references":[{"url":"https://cert-portal.siemens.com/productcert/html/ssa-032379.html"}],"providerMetadata":{"shortName":"siemens-SADP","orgId":"0b142b55-0307-4c5a-b3c9-f314f3fb7c5e","dateUpdated":"2026-05-12T12:06:04.160Z"},"x_adpType":"supplier"},{"title":"CISA ADP Vulnrichment","metrics":[{"other":{"type":"ssvc","content":{"id":"CVE-2025-39673","role":"CISA Coordinator","options":[{"Exploitation":"none"},{"Automatable":"yes"},{"Technical Impact":"total"}],"version":"2.0.3","timestamp":"2026-10-15T21:53:10.266228Z"}}}],"providerMetadata":{"shortName":"CISA-ADP","orgId":"134c704f-9b21-4f2e-91b3-4a467353bcc0","dateUpdated":"2026-10-15T22:02:29.786Z"}}]}}}