{ "dataType": "CVE_RECORD", "dataVersion": "5.2", "cveMetadata": { "cveId": "CVE-2025-39851", "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "state": "PUBLISHED", "assignerShortName": "Linux", "dateReserved": "2025-04-16T07:20:57.142Z", "datePublished": "2025-09-19T15:26:23.576Z", "dateUpdated": "2026-08-05T12:05:38.080Z" }, "containers": { "cna": { "providerMetadata": { "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "shortName": "Linux", "dateUpdated": "2026-08-05T12:05:38.080Z" }, "descriptions": [ { "lang": "en", "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nvxlan: Fix NPD when refreshing an FDB entry with a nexthop object\n\nVXLAN FDB entries can point to either a remote destination or an FDB\nnexthop group. The latter is usually used in EVPN deployments where\nlearning is disabled.\n\nHowever, when learning is enabled, an incoming packet might try to\nrefresh an FDB entry that points to an FDB nexthop group and therefore\ndoes not have a remote. Such packets should be dropped, but they are\nonly dropped after dereferencing the non-existent remote, resulting in a\nNPD [1] which can be reproduced using [2].\n\nFix by dropping such packets earlier. Remove the misleading comment from\nfirst_remote_rcu().\n\n[1]\nBUG: kernel NULL pointer dereference, address: 0000000000000000\n[...]\nCPU: 13 UID: 0 PID: 361 Comm: mausezahn Not tainted 6.17.0-rc1-virtme-g9f6b606b6b37 #1 PREEMPT(voluntary)\nHardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.17.0-4.fc41 04/01/2014\nRIP: 0010:vxlan_snoop+0x98/0x1e0\n[...]\nCall Trace:\n \n vxlan_encap_bypass+0x209/0x240\n encap_bypass_if_local+0xb1/0x100\n vxlan_xmit_one+0x1375/0x17e0\n vxlan_xmit+0x6b4/0x15f0\n dev_hard_start_xmit+0x5d/0x1c0\n __dev_queue_xmit+0x246/0xfd0\n packet_sendmsg+0x113a/0x1850\n __sock_sendmsg+0x38/0x70\n __sys_sendto+0x126/0x180\n __x64_sys_sendto+0x24/0x30\n do_syscall_64+0xa4/0x260\n entry_SYSCALL_64_after_hwframe+0x4b/0x53\n\n[2]\n #!/bin/bash\n\n ip address add 192.0.2.1/32 dev lo\n ip address add 192.0.2.2/32 dev lo\n\n ip nexthop add id 1 via 192.0.2.3 fdb\n ip nexthop add id 10 group 1 fdb\n\n ip link add name vx0 up type vxlan id 10010 local 192.0.2.1 dstport 12345 localbypass\n ip link add name vx1 up type vxlan id 10020 local 192.0.2.2 dstport 54321 learning\n\n bridge fdb add 00:11:22:33:44:55 dev vx0 self static dst 192.0.2.2 port 54321 vni 10020\n bridge fdb add 00:aa:bb:cc:dd:ee dev vx1 self static nhid 10\n\n mausezahn vx0 -a 00:aa:bb:cc:dd:ee -b 00:11:22:33:44:55 -c 1 -q" } ], "metrics": [ { "cvssV3_1": { "version": "3.1", "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H", "baseScore": 7.5, "baseSeverity": "HIGH" }, "scenarios": [ { "lang": "en", "value": "AV:N - `vxlan_rcv` is the UDP tunnel `encap_rcv` handler, so a single crafted VXLAN datagram sent to the VTEP's UDP port from anywhere routable reaches `vxlan_set_mac` → `vxlan_snoop` with a fully attacker-chosen inner source MAC. VXLAN underlays are L3-routed, so the attacker is not confined to the local segment.\nAC:L - One unsolicited packet whose inner source MAC matches an nh-backed FDB entry triggers the NULL dereference deterministically — no race, no memory-layout grooming, no timing window. Learning is the kernel default for new VXLAN devices and nexthop-backed FDB entries are standard EVPN programming, so the required state is ordinary deployment configuration rather than a condition outside the attacker's control.\nPR:N - VXLAN carries no authentication and `vxlan_rcv` performs no source-address or peer validation before handing the inner frame to `vxlan_snoop`. An entirely unauthenticated off-box attacker needs no credentials or account on the target.\nUI:N - The crash happens during packet receive processing with no involvement from any local user or administrator. No victim action of any kind is required.\nS:U - The fault occurs in the kernel and its impact is confined to that same kernel's security authority. No VM, IOMMU, or sandbox boundary is crossed.\nC:N - The dereference is a read of `remote_ip` at offset 0 (and `remote_ifindex` nearby) from a NULL pointer, well inside the unmapped guard page, so no data is read or returned to the attacker. Nothing is disclosed before the fault aborts execution.\nI:N - Execution faults at the read in `vxlan_addr_equal()`, before the `rdst->remote_ip = *src_ip` assignment, so no write or state modification ever occurs. This is a pure NULL-pointer read with no corruption or control-flow primitive.\nA:H - The NULL dereference oopses in softirq/NAPI context, which takes the `in_interrupt()` path in `die()` and panics the machine (\"Fatal exception in interrupt\") rather than merely killing a task. A remote attacker can repeat the single triggering packet at will for a persistent whole-system denial of service." } ] } ], "affected": [ { "product": "Linux", "vendor": "Linux", "defaultStatus": "unaffected", "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git", "programFiles": [ "drivers/net/vxlan/vxlan_core.c", "drivers/net/vxlan/vxlan_private.h" ], "versions": [ { "version": "1274e1cc42264d4e629841e4f182795cb0becfd2", "lessThan": "4ff4f3104da6507e0f118c63c4560dfdeb59dce3", "status": "affected", "versionType": "git" }, { "version": "1274e1cc42264d4e629841e4f182795cb0becfd2", "lessThan": "0e8630f24c14d9c655d19eabe2e52a9e9f713307", "status": "affected", "versionType": "git" }, { "version": "1274e1cc42264d4e629841e4f182795cb0becfd2", "lessThan": "6ead38147ebb813f08be6ea8ef547a0e4c09559a", "status": "affected", "versionType": "git" } ] }, { "product": "Linux", "vendor": "Linux", "defaultStatus": "affected", "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git", "programFiles": [ "drivers/net/vxlan/vxlan_core.c", "drivers/net/vxlan/vxlan_private.h" ], "versions": [ { "version": "5.8", "status": "affected" }, { "version": "0", "lessThan": "5.8", "status": "unaffected", "versionType": "semver" }, { "version": "6.12.46", "lessThanOrEqual": "6.12.*", "status": "unaffected", "versionType": "semver" }, { "version": "6.16.6", "lessThanOrEqual": "6.16.*", "status": "unaffected", "versionType": "semver" }, { "version": "6.17", "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": "5.8", "versionEndExcluding": "6.12.46" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "5.8", "versionEndExcluding": "6.16.6" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "5.8", "versionEndExcluding": "6.17" } ] } ] } ], "references": [ { "url": "https://git.kernel.org/stable/c/4ff4f3104da6507e0f118c63c4560dfdeb59dce3" }, { "url": "https://git.kernel.org/stable/c/0e8630f24c14d9c655d19eabe2e52a9e9f713307" }, { "url": "https://git.kernel.org/stable/c/6ead38147ebb813f08be6ea8ef547a0e4c09559a" } ], "title": "vxlan: Fix NPD when refreshing an FDB entry with a nexthop object", "x_generator": { "engine": "bippy-1.2.0" } }, "adp": [ { "metrics": [ { "cvssV3_1": { "scope": "UNCHANGED", "version": "3.1", "baseScore": 5.5, "attackVector": "LOCAL", "baseSeverity": "MEDIUM", "vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H", "integrityImpact": "NONE", "userInteraction": "NONE", "attackComplexity": "LOW", "availabilityImpact": "HIGH", "privilegesRequired": "LOW", "confidentialityImpact": "NONE" } }, { "other": { "type": "ssvc", "content": { "id": "CVE-2025-39851", "role": "CISA Coordinator", "options": [ { "Exploitation": "none" }, { "Automatable": "no" }, { "Technical Impact": "partial" } ], "version": "2.0.3", "timestamp": "2026-01-14T19:21:10.346641Z" } } } ], "problemTypes": [ { "descriptions": [ { "lang": "en", "type": "CWE", "cweId": "CWE-476", "description": "CWE-476 NULL Pointer Dereference" } ] } ], "title": "CISA ADP Vulnrichment", "providerMetadata": { "orgId": "134c704f-9b21-4f2e-91b3-4a467353bcc0", "shortName": "CISA-ADP", "dateUpdated": "2026-01-14T19:23:12.460Z" } } ] } }