CVE-2025-40173

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A purely remote attacker cannot create the required tunnel topology, so the reliable, fully attacker-controlled path is local.\nAC:L - The attacker controls every precondition \u2014 tunnel creation, the looping routes, and the packet stream \u2014 and each transmitted packet deterministically increments `dev->needed_headroom` until the u16 header offset wraps; no race, memory-layout luck, or victim state is involved.\nPR:L - Configuring ip6tnl/ip6gre devices and routes needs CAP_NET_ADMIN, but an unprivileged user gains that in their own network namespace with `unshare -Urn`, and the resulting heap corruption is not confined to that namespace.\nUI:N - The attacker creates the tunnels and generates the traffic itself; no action by any other user or administrator is required.\nS:U - The corruption occurs in kernel memory within the same security authority; there is no VM, IOMMU, or hypervisor boundary crossed, making this standard in-kernel privilege escalation.\nC:H - Once `network_header` wraps, `skb->data` points outside `skb->head`, producing out-of-bounds/use-after-free reads \u2014 the IPv4 twin of this bug was reported as a KASAN use-after-free read in `__skb_flow_dissect`, and such reads can disclose arbitrary adjacent kernel heap contents.\nI:H - After the negative `__skb_pull`, `dev_hard_header()` pushes and writes an L2 header at the out-of-bounds `skb->data`, giving an out-of-bounds write into unrelated kernel heap memory that can be leveraged for control-flow hijacking.\nA:H - The wrapped offsets and out-of-bounds accesses reliably produce kernel oops/panic, and the runaway headroom also forces ever-larger skb head reallocations, exhausting memory and destabilizing the system."}]}], "affected": [{"product": "Linux", "vendor": "Linux", "defaultStatus": "unaffected", "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git", "programFiles": ["include/net/ip_tunnels.h", "net/ipv4/ip_tunnel.c", "net/ipv6/ip6_tunnel.c"], 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{"version": "6.1.158", "lessThanOrEqual": "6.1.*", "status": "unaffected", "versionType": "semver"}, {"version": "6.6.114", "lessThanOrEqual": "6.6.*", "status": "unaffected", "versionType": "semver"}, {"version": "6.12.55", "lessThanOrEqual": "6.12.*", "status": "unaffected", "versionType": "semver"}, {"version": "6.17.5", "lessThanOrEqual": "6.17.*", "status": "unaffected", "versionType": "semver"}, {"version": "6.18", "lessThanOrEqual": "*", "status": "unaffected", "versionType": "original_commit_for_fix"}]}], "cpeApplicability": [{"nodes": [{"operator": "OR", "negate": false, "cpeMatch": [{"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "4.7", "versionEndExcluding": "5.4.301"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "4.7", "versionEndExcluding": "5.10.246"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", 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{"url": "https://git.kernel.org/stable/c/402b6985e872b4cf394bbbf33b503947a326a6cb"}, {"url": "https://git.kernel.org/stable/c/10fe967efe73c610e526ff7460581610633dee9c"}, {"url": "https://git.kernel.org/stable/c/48294a67863c9cfa367abb66bbf0ef6548ae124f"}, {"url": "https://git.kernel.org/stable/c/eeb4345488672584db4f8c20a1ae13a212ce31c4"}, {"url": "https://git.kernel.org/stable/c/b6eb25d870f1a8ae571fd3da2244b71df547824b"}, {"url": "https://git.kernel.org/stable/c/21f4d45eba0b2dcae5dbc9e5e0ad08735c993f16"}], "title": "net/ip6_tunnel: Prevent perpetual tunnel growth", "x_generator": {"engine": "bippy-1.2.0"}}, "adp": [{"metrics": [{"other": {"type": "ssvc", "content": {"id": "CVE-2025-40173", "role": "CISA Coordinator", "options": [{"Exploitation": "none"}, {"Automatable": "no"}, {"Technical Impact": "total"}], "version": "2.0.3", "timestamp": "2026-10-15T21:57:37.658529Z"}}}], "title": "CISA ADP Vulnrichment", "providerMetadata": {"orgId": "134c704f-9b21-4f2e-91b3-4a467353bcc0", "shortName": "CISA-ADP", "dateUpdated": "2026-10-15T22:02:39.584Z"}}]}}

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A purely remote attacker cannot create the required tunnel topology, so the reliable, fully attacker-controlled path is local.\nAC:L - The attacker controls every precondition \u2014 tunnel creation, the looping routes, and the packet stream \u2014 and each transmitted packet deterministically increments `dev->needed_headroom` until the u16 header offset wraps; no race, memory-layout luck, or victim state is involved.\nPR:L - Configuring ip6tnl/ip6gre devices and routes needs CAP_NET_ADMIN, but an unprivileged user gains that in their own network namespace with `unshare -Urn`, and the resulting heap corruption is not confined to that namespace.\nUI:N - The attacker creates the tunnels and generates the traffic itself; no action by any other user or administrator is required.\nS:U - The corruption occurs in kernel memory within the same security authority; there is no VM, IOMMU, or hypervisor boundary crossed, making this standard in-kernel privilege escalation.\nC:H - Once `network_header` wraps, `skb->data` points outside `skb->head`, producing out-of-bounds/use-after-free reads \u2014 the IPv4 twin of this bug was reported as a KASAN use-after-free read in `__skb_flow_dissect`, and such reads can disclose arbitrary adjacent kernel heap contents.\nI:H - After the negative `__skb_pull`, `dev_hard_header()` pushes and writes an L2 header at the out-of-bounds `skb->data`, giving an out-of-bounds write into unrelated kernel heap memory that can be leveraged for control-flow hijacking.\nA:H - The wrapped offsets and out-of-bounds accesses reliably produce kernel oops/panic, and the runaway headroom also forces ever-larger skb head reallocations, exhausting memory and destabilizing the system."}]}], "affected": [{"repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git", "vendor": "Linux", "product": "Linux", "versions": [{"status": "affected", "version": "8eb30be0352d09165e94a41fef1c7b994dca0714", "lessThan": 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"https://git.kernel.org/stable/c/eeb4345488672584db4f8c20a1ae13a212ce31c4"}, {"url": "https://git.kernel.org/stable/c/b6eb25d870f1a8ae571fd3da2244b71df547824b"}, {"url": "https://git.kernel.org/stable/c/21f4d45eba0b2dcae5dbc9e5e0ad08735c993f16"}], "x_generator": {"engine": "bippy-1.2.0"}, "descriptions": [{"lang": "en", "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nnet/ip6_tunnel: Prevent perpetual tunnel growth\n\nSimilarly to ipv4 tunnel, ipv6 version updates dev->needed_headroom, too.\nWhile ipv4 tunnel headroom adjustment growth was limited in\ncommit 5ae1e9922bbd (\"net: ip_tunnel: prevent perpetual headroom growth\"),\nipv6 tunnel yet increases the headroom without any ceiling.\n\nReflect ipv4 tunnel headroom adjustment limit on ipv6 version.\n\nCredits to Francesco Ruggeri, who was originally debugging this issue\nand wrote local Arista-specific patch and a reproducer."}], "cpeApplicability": [{"nodes": [{"negate": false, "cpeMatch": 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{"affected": [{"affectedData": [{"defaultStatus": "unaffected", "product": "Linux", "programFiles": ["include/net/ip_tunnels.h", "net/ipv4/ip_tunnel.c", "net/ipv6/ip6_tunnel.c"], "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git", "vendor": "Linux", "versions": [{"lessThan": "566f8d5c8a443f2dd69c5460fdec43ed1c870c65", "status": "affected", "version": "8eb30be0352d09165e94a41fef1c7b994dca0714", "versionType": "git"}, {"lessThan": "11f6066af3bfb8149aa16c42c0b0c5ea5b199a94", "status": "affected", "version": "8eb30be0352d09165e94a41fef1c7b994dca0714", "versionType": "git"}, {"lessThan": "402b6985e872b4cf394bbbf33b503947a326a6cb", "status": "affected", "version": "8eb30be0352d09165e94a41fef1c7b994dca0714", "versionType": "git"}, {"lessThan": "10fe967efe73c610e526ff7460581610633dee9c", "status": "affected", "version": "8eb30be0352d09165e94a41fef1c7b994dca0714", "versionType": "git"}, {"lessThan": "48294a67863c9cfa367abb66bbf0ef6548ae124f", "status": "affected", 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"5.4.301", "versionType": "semver"}, {"lessThanOrEqual": "5.10.*", "status": "unaffected", "version": "5.10.246", "versionType": "semver"}, {"lessThanOrEqual": "5.15.*", "status": "unaffected", "version": "5.15.196", "versionType": "semver"}, {"lessThanOrEqual": "6.1.*", "status": "unaffected", "version": "6.1.158", "versionType": "semver"}, {"lessThanOrEqual": "6.6.*", "status": "unaffected", "version": "6.6.114", "versionType": "semver"}, {"lessThanOrEqual": "6.12.*", "status": "unaffected", "version": "6.12.55", "versionType": "semver"}, {"lessThanOrEqual": "6.17.*", "status": "unaffected", "version": "6.17.5", "versionType": "semver"}, {"lessThanOrEqual": "*", "status": "unaffected", "version": "6.18", "versionType": "original_commit_for_fix"}]}], "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"}], "cveTags": [], "descriptions": [{"lang": "en", "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nnet/ip6_tunnel: Prevent perpetual tunnel growth\n\nSimilarly to ipv4 tunnel, ipv6 version updates dev->needed_headroom, too.\nWhile ipv4 tunnel headroom adjustment growth was limited in\ncommit 5ae1e9922bbd (\"net: ip_tunnel: prevent perpetual headroom growth\"),\nipv6 tunnel yet increases the headroom without any ceiling.\n\nReflect ipv4 tunnel headroom adjustment limit on ipv6 version.\n\nCredits to Francesco Ruggeri, who was originally debugging this issue\nand wrote local Arista-specific patch and a reproducer."}, {"lang": "es", "value": "En el kernel de Linux, la siguiente vulnerabilidad ha sido resuelta:\n\nnet/ip6_tunnel: Prevenir el crecimiento perpetuo del t\u00fanel\n\nDe manera similar al t\u00fanel ipv4, la versi\u00f3n ipv6 tambi\u00e9n actualiza dev->needed_headroom.\nMientras que el crecimiento del ajuste del headroom del t\u00fanel ipv4 fue limitado en el commit 5ae1e9922bbd (\u201cnet: ip_tunnel: prevenir el crecimiento perpetuo del headroom\u201d), el t\u00fanel ipv6 a\u00fan aumenta el headroom sin ning\u00fan techo.\n\nReflejar el l\u00edmite de ajuste del headroom del t\u00fanel ipv4 en la versi\u00f3n ipv6.\n\nCr\u00e9ditos a Francesco Ruggeri, quien originalmente estaba depurando este problema y escribi\u00f3 un parche local espec\u00edfico de Arista y un reproductor."}], "id": "CVE-2025-40173", "lastModified": "2026-10-19T21:10:00.160", "metrics": {"cvssMetricV31": [{"cvssData": {"attackComplexity": "LOW", "attackVector": "LOCAL", "availabilityImpact": "HIGH", "baseScore": 7.8, "baseSeverity": "HIGH", "confidentialityImpact": "HIGH", "integrityImpact": "HIGH", "privilegesRequired": "LOW", "scope": "UNCHANGED", "userInteraction": "NONE", "vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H", "version": "3.1"}, "exploitabilityScore": 1.8, "impactScore": 5.9, "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "type": "Secondary"}], "ssvcV203": [{"source": "134c704f-9b21-4f2e-91b3-4a467353bcc0", "ssvcData": {"id": "CVE-2025-40173", "options": [{"exploitation": "none"}, {"automatable": "no"}, {"technicalImpact": "total"}], "role": "CISA Coordinator", "timestamp": "2026-10-15T21:57:37.658529Z", "version": "2.0.3"}}]}, "published": "2025-11-12T11:15:47.780", "references": [{"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "url": "https://git.kernel.org/stable/c/10fe967efe73c610e526ff7460581610633dee9c"}, {"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "url": "https://git.kernel.org/stable/c/11f6066af3bfb8149aa16c42c0b0c5ea5b199a94"}, {"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "url": "https://git.kernel.org/stable/c/21f4d45eba0b2dcae5dbc9e5e0ad08735c993f16"}, {"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "url": "https://git.kernel.org/stable/c/402b6985e872b4cf394bbbf33b503947a326a6cb"}, {"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "url": "https://git.kernel.org/stable/c/48294a67863c9cfa367abb66bbf0ef6548ae124f"}, {"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "url": "https://git.kernel.org/stable/c/566f8d5c8a443f2dd69c5460fdec43ed1c870c65"}, {"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "url": "https://git.kernel.org/stable/c/b6eb25d870f1a8ae571fd3da2244b71df547824b"}, {"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "url": "https://git.kernel.org/stable/c/eeb4345488672584db4f8c20a1ae13a212ce31c4"}], "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "vulnStatus": "Deferred"}

{"bugzilla": {"description": "kernel: net/ip6_tunnel: Prevent perpetual tunnel growth", "id": "2414492", "url": "https://bugzilla.redhat.com/show_bug.cgi?id=2414492"}, "csaw": false, "cvss3": {"cvss3_base_score": "7.0", "cvss3_scoring_vector": "CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H", "status": "draft"}, "details": ["In the Linux kernel, the following vulnerability has been resolved:\nnet/ip6_tunnel: Prevent perpetual tunnel growth\nSimilarly to ipv4 tunnel, ipv6 version updates dev->needed_headroom, too.\nWhile ipv4 tunnel headroom adjustment growth was limited in\ncommit 5ae1e9922bbd (\"net: ip_tunnel: prevent perpetual headroom growth\"),\nipv6 tunnel yet increases the headroom without any ceiling.\nReflect ipv4 tunnel headroom adjustment limit on ipv6 version.\nCredits to Francesco Ruggeri, who was originally debugging this issue\nand wrote local Arista-specific patch and a reproducer."], "name": "CVE-2025-40173", "package_state": [{"cpe": "cpe:/o:redhat:enterprise_linux:10", "fix_state": "Affected", "package_name": "kernel", "product_name": "Red Hat Enterprise Linux 10"}, {"cpe": "cpe:/o:redhat:enterprise_linux:6", "fix_state": "Out of support scope", "package_name": "kernel", "product_name": "Red Hat Enterprise Linux 6"}, {"cpe": "cpe:/o:redhat:enterprise_linux:7", "fix_state": "Affected", "package_name": "kernel", "product_name": "Red Hat Enterprise Linux 7"}, {"cpe": "cpe:/o:redhat:enterprise_linux:7", "fix_state": "Affected", "package_name": "kernel-rt", "product_name": "Red Hat Enterprise Linux 7"}, {"cpe": "cpe:/o:redhat:enterprise_linux:8", "fix_state": "Affected", "package_name": "kernel", "product_name": "Red Hat Enterprise Linux 8"}, {"cpe": "cpe:/o:redhat:enterprise_linux:8", "fix_state": "Affected", "package_name": "kernel-rt", "product_name": "Red Hat Enterprise Linux 8"}, {"cpe": "cpe:/o:redhat:enterprise_linux:9", "fix_state": "Affected", "package_name": "kernel", "product_name": "Red Hat Enterprise Linux 9"}, {"cpe": "cpe:/o:redhat:enterprise_linux:9", "fix_state": "Affected", "package_name": "kernel-rt", "product_name": "Red Hat Enterprise Linux 9"}], "public_date": "2025-11-12T00:00:00Z", "references": ["https://www.cve.org/CVERecord?id=CVE-2025-40173\nhttps://nvd.nist.gov/vuln/detail/CVE-2025-40173\nhttps://lore.kernel.org/linux-cve-announce/2025111254-CVE-2025-40173-4a68@gregkh/T"], "threat_severity": "Moderate"}

{"created": "2025-11-12T22:12:25.417683+00:00", "updated": "2025-11-12T22:12:25.417709+00:00", "vendors": ["linux", "linux$PRODUCT$linux_kernel"]}