CVE-2026-89555 (GCVE-0-2026-89555)
Vulnerability from cvelistv5
Published
2026-09-11 19:44
Modified
2026-10-19 08:48
Severity ?
9.8 (Critical) - CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Summary
In the Linux kernel, the following vulnerability has been resolved: mpls: reload header after pskb_may_pull() mpls_select_multipath() calls mpls_multipath_hash() to choose a nexthop when an MPLS route has multiple nexthops. While walking the MPLS label stack, the hash routine caches hdr for the current label. After finding the bottom-of-stack label, it calls pskb_may_pull() before reading the inner IP header. If an skb is constructed with the inner IP header in nonlinear data and insufficient tailroom in the linear head, pskb_may_pull() calls pskb_expand_head() to replace the skb head and free the old one. This leaves hdr pointing to freed memory. The IPv6 path can invalidate hdr again when it performs a second pull for the larger header. The issue was found through static analysis. A reproducer sending a legal Geneve packet through a bareudp/MPLS multipath setup triggered the same KASAN report in 2 of 2 unpatched runs: BUG: KASAN: slab-use-after-free in mpls_select_multipath Read of size 1 at addr ffff88800ecc6e20 by task ksoftirqd/1/23 Call Trace: mpls_select_multipath mpls_forward __netif_receive_skb_list_core netif_receive_skb_list_internal napi_complete_done gro_cell_poll __napi_poll net_rx_action Freed by task 23: kfree pskb_expand_head __pskb_pull_tail mpls_select_multipath Reload hdr from the current skb head after each successful pull before deriving the inner IPv4 or IPv6 header pointer.
References
Impacted products
Vendor Product Version
Linux Linux Version: 9f427a0e474a67b454420c131709600d44850486
Version: 9f427a0e474a67b454420c131709600d44850486
Version: 9f427a0e474a67b454420c131709600d44850486
Version: 9f427a0e474a67b454420c131709600d44850486
Version: 9f427a0e474a67b454420c131709600d44850486
Version: 9f427a0e474a67b454420c131709600d44850486
Version: 9f427a0e474a67b454420c131709600d44850486
Version: 9f427a0e474a67b454420c131709600d44850486
Version: ad864d9fce0ec56cc8f6afe5c6a0e6d7f484b9eb
Version: 4.9.8   ≤
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          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nmpls: reload header after pskb_may_pull()\n\nmpls_select_multipath() calls mpls_multipath_hash() to choose a nexthop\nwhen an MPLS route has multiple nexthops.  While walking the MPLS label\nstack, the hash routine caches hdr for the current label.  After finding\nthe bottom-of-stack label, it calls pskb_may_pull() before reading the\ninner IP header.\n\nIf an skb is constructed with the inner IP header in nonlinear data and\ninsufficient tailroom in the linear head, pskb_may_pull() calls\npskb_expand_head() to replace the skb head and free the old one.  This\nleaves hdr pointing to freed memory.  The IPv6 path can invalidate hdr\nagain when it performs a second pull for the larger header.\n\nThe issue was found through static analysis.  A reproducer sending a legal\nGeneve packet through a bareudp/MPLS multipath setup triggered the same\nKASAN report in 2 of 2 unpatched runs:\n\n  BUG: KASAN: slab-use-after-free in mpls_select_multipath\n  Read of size 1 at addr ffff88800ecc6e20 by task ksoftirqd/1/23\n\n  Call Trace:\n   mpls_select_multipath\n   mpls_forward\n   __netif_receive_skb_list_core\n   netif_receive_skb_list_internal\n   napi_complete_done\n   gro_cell_poll\n   __napi_poll\n   net_rx_action\n\n  Freed by task 23:\n   kfree\n   pskb_expand_head\n   __pskb_pull_tail\n   mpls_select_multipath\n\nReload hdr from the current skb head after each successful pull before\nderiving the inner IPv4 or IPv6 header pointer."
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              "value": "AV:N - mpls_forward() is the ETH_P_MPLS_UC packet_type receive handler; remote MPLS-in-IP (IPPROTO_MPLS), MPLS-over-UDP/bareudp, Geneve, and IPIP/SIT/ip6 tunnels deliver inner MPLS into this path without local access, matching the Geneve/bareudp KASAN reproducer.\nAC:L - An attacker sending MPLS or tunneled overlay frames fully controls the label stack, BOS bit, and skb layout; GRO/tunnel decap yields nonlinear skbs so pskb_may_pull() reallocates skb-\u003ehead, and the unpatched Geneve reproducer hit the UAF in 2 of 2 runs with no victim-timed race.\nPR:N - Exploitation needs only unauthenticated packets that hit an already configured MPLS-enabled interface and multipath label route; mpls_forward() performs no credential check, and enabling MPLS input or tunnels is victim deployment rather than an attacker privilege.\nUI:N - The use-after-free runs in softirq receive processing (gro_cell_poll / netif_receive_skb_list) as soon as the crafted frame is accepted; no local user or administrator action is required beyond normal forwarding.\nS:U - The stale MPLS header pointer is a heap use-after-free inside the same host kernel MPLS forwarding path; impact stays within that kernel security authority and does not cross a VM, IOMMU, or other boundary.\nC:H - After pskb_expand_head() frees the old skb head, mpls_multipath_hash() reads the inner IPv4/IPv6 header through the stale hdr pointer, a slab use-after-free that can disclose freed kmalloc contents and is scored as high-impact kernel information disclosure.\nI:H - The immediate stale access is a header read used for ECMP hashing, but it remains a kernel slab use-after-free of skb-\u003ehead; attacker-controlled reclaim of the freed kmalloc object is a well-established path to heap corruption and control-flow hijacking.\nA:H - KASAN confirmed a slab-use-after-free in mpls_select_multipath() on the forwarding path; dereferencing the freed skb head can oops or panic the kernel, and UAFs remain a high-impact denial of service even without full exploitation."
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    "assignerShortName": "Linux",
    "cveId": "CVE-2026-89555",
    "datePublished": "2026-09-11T19:44:28.331Z",
    "dateReserved": "2026-09-11T19:38:34.724Z",
    "dateUpdated": "2026-10-19T08:48:48.093Z",
    "state": "PUBLISHED"
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GRO/tunnel decap yields nonlinear skbs so pskb_may_pull() reallocates skb-\u003ehead, and the unpatched Geneve reproducer hit the UAF in 2 of 2 runs with no victim-timed race.\\nPR:N - Exploitation needs only unauthenticated packets that hit an already configured MPLS-enabled interface and multipath label route; mpls_forward() performs no credential check, and enabling MPLS input or tunnels is victim deployment rather than an attacker privilege.\\nUI:N - The use-after-free runs in softirq receive processing (gro_cell_poll / netif_receive_skb_list) as soon as the crafted frame is accepted; no local user or administrator action is required beyond normal forwarding.\\nS:U - The stale MPLS header pointer is a heap use-after-free inside the same host kernel MPLS forwarding path; impact stays within that kernel security authority and does not cross a VM, IOMMU, or other boundary.\\nC:H - After pskb_expand_head() frees the old skb head, mpls_multipath_hash() reads the inner IPv4/IPv6 header through the stale hdr pointer, a slab use-after-free that can disclose freed kmalloc contents and is scored as high-impact kernel information disclosure.\\nI:H - The immediate stale access is a header read used for ECMP hashing, but it remains a kernel slab use-after-free of skb-\u003ehead; attacker-controlled reclaim of the freed kmalloc object is a well-established path to heap corruption and control-flow hijacking.\\nA:H - KASAN confirmed a slab-use-after-free in mpls_select_multipath() on the forwarding path; dereferencing the freed skb head can oops or panic the kernel, and UAFs remain a high-impact denial of service even without full exploitation.\"}]}], \"affected\": [{\"repo\": \"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git\", \"vendor\": \"Linux\", \"product\": \"Linux\", \"versions\": [{\"status\": \"affected\", \"version\": \"9f427a0e474a67b454420c131709600d44850486\", \"lessThan\": \"aa4fe0b450a461aa1162fe8375f5d28f4c957df8\", \"versionType\": \"git\"}, {\"status\": \"affected\", \"version\": \"9f427a0e474a67b454420c131709600d44850486\", \"lessThan\": \"b1c0783b2facc398437ad8f8b86c636d7a78f8db\", \"versionType\": \"git\"}, {\"status\": \"affected\", \"version\": \"9f427a0e474a67b454420c131709600d44850486\", \"lessThan\": \"bfaaff99238326166694354a63a76c02563f98b1\", \"versionType\": \"git\"}, {\"status\": \"affected\", \"version\": \"9f427a0e474a67b454420c131709600d44850486\", \"lessThan\": \"d9640239827d6d0cb84263b590f7a4f1596c17eb\", \"versionType\": \"git\"}, {\"status\": \"affected\", \"version\": \"9f427a0e474a67b454420c131709600d44850486\", \"lessThan\": \"fed638a248116b8a249bd4202d28e5934bdc65ad\", \"versionType\": \"git\"}, {\"status\": \"affected\", \"version\": \"9f427a0e474a67b454420c131709600d44850486\", \"lessThan\": \"d82b90a38c2ca8a0694428eab0e9551c23f2447d\", \"versionType\": \"git\"}, {\"status\": \"affected\", \"version\": \"9f427a0e474a67b454420c131709600d44850486\", \"lessThan\": \"49d38c1b4390412f8950d33dfaee0ccbd17beb81\", \"versionType\": \"git\"}, {\"status\": \"affected\", \"version\": \"9f427a0e474a67b454420c131709600d44850486\", \"lessThan\": \"29e63b8d9fc150cc191b1c6eb7e16e1247e1b650\", \"versionType\": \"git\"}, {\"status\": \"affected\", \"version\": \"ad864d9fce0ec56cc8f6afe5c6a0e6d7f484b9eb\", \"versionType\": \"git\"}, {\"status\": \"affected\", \"version\": \"4.9.8\", \"lessThan\": \"4.10\", \"versionType\": \"semver\"}], \"programFiles\": [\"net/mpls/af_mpls.c\"], \"defaultStatus\": \"unaffected\"}, {\"repo\": \"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git\", \"vendor\": \"Linux\", \"product\": \"Linux\", \"versions\": [{\"status\": \"affected\", \"version\": \"4.10\"}, {\"status\": \"unaffected\", \"version\": \"0\", \"lessThan\": \"4.10\", \"versionType\": \"semver\"}, {\"status\": \"unaffected\", \"version\": \"5.10.270\", \"versionType\": \"semver\", \"lessThanOrEqual\": \"5.10.*\"}, {\"status\": \"unaffected\", \"version\": \"5.15.221\", \"versionType\": \"semver\", \"lessThanOrEqual\": \"5.15.*\"}, {\"status\": \"unaffected\", \"version\": \"6.1.188\", \"versionType\": \"semver\", \"lessThanOrEqual\": \"6.1.*\"}, {\"status\": \"unaffected\", \"version\": \"6.6.157\", \"versionType\": \"semver\", \"lessThanOrEqual\": \"6.6.*\"}, {\"status\": \"unaffected\", \"version\": \"6.12.109\", \"versionType\": \"semver\", \"lessThanOrEqual\": \"6.12.*\"}, {\"status\": \"unaffected\", \"version\": \"6.18.50\", \"versionType\": \"semver\", \"lessThanOrEqual\": \"6.18.*\"}, {\"status\": \"unaffected\", \"version\": \"7.2.4\", \"versionType\": \"semver\", \"lessThanOrEqual\": \"7.2.*\"}, {\"status\": \"unaffected\", \"version\": \"7.3\", \"versionType\": \"original_commit_for_fix\", \"lessThanOrEqual\": \"*\"}], \"programFiles\": [\"net/mpls/af_mpls.c\"], \"defaultStatus\": \"affected\"}], \"references\": [{\"url\": \"https://git.kernel.org/stable/c/aa4fe0b450a461aa1162fe8375f5d28f4c957df8\"}, {\"url\": \"https://git.kernel.org/stable/c/b1c0783b2facc398437ad8f8b86c636d7a78f8db\"}, {\"url\": \"https://git.kernel.org/stable/c/bfaaff99238326166694354a63a76c02563f98b1\"}, {\"url\": \"https://git.kernel.org/stable/c/d9640239827d6d0cb84263b590f7a4f1596c17eb\"}, {\"url\": \"https://git.kernel.org/stable/c/fed638a248116b8a249bd4202d28e5934bdc65ad\"}, {\"url\": \"https://git.kernel.org/stable/c/d82b90a38c2ca8a0694428eab0e9551c23f2447d\"}, {\"url\": \"https://git.kernel.org/stable/c/49d38c1b4390412f8950d33dfaee0ccbd17beb81\"}, {\"url\": \"https://git.kernel.org/stable/c/29e63b8d9fc150cc191b1c6eb7e16e1247e1b650\"}], \"x_generator\": {\"engine\": \"bippy-1.2.0\"}, \"descriptions\": [{\"lang\": \"en\", \"value\": \"In the Linux kernel, the following vulnerability has been resolved:\\n\\nmpls: reload header after pskb_may_pull()\\n\\nmpls_select_multipath() calls mpls_multipath_hash() to choose a nexthop\\nwhen an MPLS route has multiple nexthops.  While walking the MPLS label\\nstack, the hash routine caches hdr for the current label.  After finding\\nthe bottom-of-stack label, it calls pskb_may_pull() before reading the\\ninner IP header.\\n\\nIf an skb is constructed with the inner IP header in nonlinear data and\\ninsufficient tailroom in the linear head, pskb_may_pull() calls\\npskb_expand_head() to replace the skb head and free the old one.  This\\nleaves hdr pointing to freed memory.  The IPv6 path can invalidate hdr\\nagain when it performs a second pull for the larger header.\\n\\nThe issue was found through static analysis.  A reproducer sending a legal\\nGeneve packet through a bareudp/MPLS multipath setup triggered the same\\nKASAN report in 2 of 2 unpatched runs:\\n\\n  BUG: KASAN: slab-use-after-free in mpls_select_multipath\\n  Read of size 1 at addr ffff88800ecc6e20 by task ksoftirqd/1/23\\n\\n  Call Trace:\\n   mpls_select_multipath\\n   mpls_forward\\n   __netif_receive_skb_list_core\\n   netif_receive_skb_list_internal\\n   napi_complete_done\\n   gro_cell_poll\\n   __napi_poll\\n   net_rx_action\\n\\n  Freed by task 23:\\n   kfree\\n   pskb_expand_head\\n   __pskb_pull_tail\\n   mpls_select_multipath\\n\\nReload hdr from the current skb head after each successful pull before\\nderiving the inner IPv4 or IPv6 header pointer.\"}], \"cpeApplicability\": [{\"nodes\": [{\"negate\": false, \"cpeMatch\": [{\"criteria\": \"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*\", \"vulnerable\": true, \"versionEndExcluding\": \"5.10.270\", \"versionStartIncluding\": \"4.10\"}, {\"criteria\": \"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*\", \"vulnerable\": true, \"versionEndExcluding\": \"5.15.221\", \"versionStartIncluding\": \"4.10\"}, {\"criteria\": \"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*\", \"vulnerable\": true, \"versionEndExcluding\": \"6.1.188\", \"versionStartIncluding\": \"4.10\"}, {\"criteria\": \"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*\", \"vulnerable\": true, \"versionEndExcluding\": \"6.6.157\", \"versionStartIncluding\": \"4.10\"}, {\"criteria\": \"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*\", \"vulnerable\": true, \"versionEndExcluding\": \"6.12.109\", \"versionStartIncluding\": \"4.10\"}, {\"criteria\": \"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*\", \"vulnerable\": true, \"versionEndExcluding\": \"6.18.50\", \"versionStartIncluding\": \"4.10\"}, {\"criteria\": \"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*\", \"vulnerable\": true, \"versionEndExcluding\": \"7.2.4\", \"versionStartIncluding\": \"4.10\"}, {\"criteria\": \"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*\", \"vulnerable\": true, \"versionEndExcluding\": \"7.3\", \"versionStartIncluding\": \"4.10\"}, {\"criteria\": \"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*\", \"vulnerable\": true, \"versionStartIncluding\": \"4.9.8\"}], \"operator\": \"OR\"}]}], \"providerMetadata\": {\"orgId\": \"416baaa9-dc9f-4396-8d5f-8c081fb06d67\", \"shortName\": \"Linux\", \"dateUpdated\": \"2026-10-19T08:48:48.093Z\"}}}",
      "cveMetadata": "{\"cveId\": \"CVE-2026-89555\", \"state\": \"PUBLISHED\", \"dateUpdated\": \"2026-10-19T08:48:48.093Z\", \"dateReserved\": \"2026-09-11T19:38:34.724Z\", \"assignerOrgId\": \"416baaa9-dc9f-4396-8d5f-8c081fb06d67\", \"datePublished\": \"2026-09-11T19:44:28.331Z\", \"assignerShortName\": \"Linux\"}",
      "dataType": "CVE_RECORD",
      "dataVersion": "5.2"
    }
  }
}


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