{ "schema_version": "1.6.1", "id": "RPI-CVE-2026-89555", "modified": "2026-10-09T11:39:44Z", "upstream": [ "CVE-2026-89555" ], "published": "2026-09-11T19:47:07Z", "summary": "mpls: reload header after pskb_may_pull()", "details": "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.", "severity": [ { "type": "CVSS_V3", "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H" } ], "affected": [ { "package": { "ecosystem": "Raspberry Pi OS:12", "name": "linux" }, "versions": [ "1:6.1.47-1+rpt4" ], "ecosystem_specific": { "binaries": [ { "binary_name": "linux-image-6.1.0-rpi3-rpi-2712", "binary_version": "1:6.1.47-1+rpt4" }, { "binary_name": "linux-image-6.1.0-rpi3-rpi-v6", "binary_version": "1:6.1.47-1+rpt4" }, { "binary_name": "linux-image-6.1.0-rpi3-rpi-v7", "binary_version": "1:6.1.47-1+rpt4" }, { "binary_name": "linux-image-6.1.0-rpi3-rpi-v7l", "binary_version": "1:6.1.47-1+rpt4" }, { "binary_name": "linux-image-6.1.0-rpi3-rpi-v8", "binary_version": "1:6.1.47-1+rpt4" } ] }, "database_specific": { "per_version": { "1:6.1.47-1+rpt4": { "linux_commit": "655fc658a15ae7a6f37103754adb39ba52a9a14e", "upstream_version": "6.1.47", "assessment": "commit ancestry (strak rule)", "upstream_fixed": "6.1.188", "compiled_filter": false } } } } ], "references": [ { "type": "ADVISORY", "url": "https://www.cve.org/CVERecord?id=CVE-2026-89555" }, { "type": "FIX", "url": "https://git.kernel.org/stable/c/aa4fe0b450a461aa1162fe8375f5d28f4c957df8" }, { "type": "FIX", "url": "https://git.kernel.org/stable/c/b1c0783b2facc398437ad8f8b86c636d7a78f8db" }, { "type": "FIX", "url": "https://git.kernel.org/stable/c/bfaaff99238326166694354a63a76c02563f98b1" }, { "type": "FIX", "url": "https://git.kernel.org/stable/c/d9640239827d6d0cb84263b590f7a4f1596c17eb" }, { "type": "FIX", "url": "https://git.kernel.org/stable/c/fed638a248116b8a249bd4202d28e5934bdc65ad" }, { "type": "FIX", "url": "https://git.kernel.org/stable/c/d82b90a38c2ca8a0694428eab0e9551c23f2447d" }, { "type": "FIX", "url": "https://git.kernel.org/stable/c/49d38c1b4390412f8950d33dfaee0ccbd17beb81" }, { "type": "FIX", "url": "https://git.kernel.org/stable/c/29e63b8d9fc150cc191b1c6eb7e16e1247e1b650" } ], "database_specific": { "source": "https://git.kernel.org/pub/scm/linux/security/vulns.git", "upstream_modified": "2026-09-14T12:06:03Z", "severity": { "source": "kernel CNA", "cvss_v3_score": 9.8, "cvss_v3_severity": "Critical", "scenario": "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->head, 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->head; 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." } } }