CVE-2025-40206 (GCVE-0-2025-40206)
Vulnerability from cvelistv5 – Published: 2025-11-12 21:56 – Updated: 2026-08-23 12:45
VLAI
EPSS
VEX
Title
netfilter: nft_objref: validate objref and objrefmap expressions
Summary
In the Linux kernel, the following vulnerability has been resolved:
netfilter: nft_objref: validate objref and objrefmap expressions
Referencing a synproxy stateful object from OUTPUT hook causes kernel
crash due to infinite recursive calls:
BUG: TASK stack guard page was hit at 000000008bda5b8c (stack is 000000003ab1c4a5..00000000494d8b12)
[...]
Call Trace:
__find_rr_leaf+0x99/0x230
fib6_table_lookup+0x13b/0x2d0
ip6_pol_route+0xa4/0x400
fib6_rule_lookup+0x156/0x240
ip6_route_output_flags+0xc6/0x150
__nf_ip6_route+0x23/0x50
synproxy_send_tcp_ipv6+0x106/0x200
synproxy_send_client_synack_ipv6+0x1aa/0x1f0
nft_synproxy_do_eval+0x263/0x310
nft_do_chain+0x5a8/0x5f0 [nf_tables
nft_do_chain_inet+0x98/0x110
nf_hook_slow+0x43/0xc0
__ip6_local_out+0xf0/0x170
ip6_local_out+0x17/0x70
synproxy_send_tcp_ipv6+0x1a2/0x200
synproxy_send_client_synack_ipv6+0x1aa/0x1f0
[...]
Implement objref and objrefmap expression validate functions.
Currently, only NFT_OBJECT_SYNPROXY object type requires validation.
This will also handle a jump to a chain using a synproxy object from the
OUTPUT hook.
Now when trying to reference a synproxy object in the OUTPUT hook, nft
will produce the following error:
synproxy_crash.nft: Error: Could not process rule: Operation not supported
synproxy name mysynproxy
^^^^^^^^^^^^^^^^^^^^^^^^
Severity
7.8 (High)
Assigner
References
Impacted products
2 products
| Vendor | Product | Version | CPE status | |
|---|---|---|---|---|
| Linux | Linux |
Affected:
ee394f96ad7517fbc0de9106dcc7ce9efb14f264 , < f31bcea12222a26d6f151df9c4a6d21f2eec1724
(git)
Affected: ee394f96ad7517fbc0de9106dcc7ce9efb14f264 , < 0028e0134c64d9ed21728341a74fcfc59cd0f944 (git) Affected: ee394f96ad7517fbc0de9106dcc7ce9efb14f264 , < 7ea55a44493a5a36c3b3293b88bbe4841f9dbaf0 (git) Affected: ee394f96ad7517fbc0de9106dcc7ce9efb14f264 , < 4c1cf72ec10be5a9ad264650cadffa1fbce6fabd (git) Affected: ee394f96ad7517fbc0de9106dcc7ce9efb14f264 , < f359b809d54c6e3dd1d039b97e0b68390b0e53e4 (git) |
guessed | |
| Linux | Linux |
Affected:
5.4
Unaffected: 0 , < 5.4 (semver) Unaffected: 6.1.184 , ≤ 6.1.* (semver) Unaffected: 6.6.113 , ≤ 6.6.* (semver) Unaffected: 6.12.54 , ≤ 6.12.* (semver) Unaffected: 6.17.4 , ≤ 6.17.* (semver) Unaffected: 6.18 , ≤ * (original_commit_for_fix) |
guessed |
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"product": "Linux",
"programFiles": [
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"descriptions": [
{
"lang": "en",
"value": "In the Linux kernel, the following vulnerability has been resolved:\n\nnetfilter: nft_objref: validate objref and objrefmap expressions\n\nReferencing a synproxy stateful object from OUTPUT hook causes kernel\ncrash due to infinite recursive calls:\n\nBUG: TASK stack guard page was hit at 000000008bda5b8c (stack is 000000003ab1c4a5..00000000494d8b12)\n[...]\nCall Trace:\n __find_rr_leaf+0x99/0x230\n fib6_table_lookup+0x13b/0x2d0\n ip6_pol_route+0xa4/0x400\n fib6_rule_lookup+0x156/0x240\n ip6_route_output_flags+0xc6/0x150\n __nf_ip6_route+0x23/0x50\n synproxy_send_tcp_ipv6+0x106/0x200\n synproxy_send_client_synack_ipv6+0x1aa/0x1f0\n nft_synproxy_do_eval+0x263/0x310\n nft_do_chain+0x5a8/0x5f0 [nf_tables\n nft_do_chain_inet+0x98/0x110\n nf_hook_slow+0x43/0xc0\n __ip6_local_out+0xf0/0x170\n ip6_local_out+0x17/0x70\n synproxy_send_tcp_ipv6+0x1a2/0x200\n synproxy_send_client_synack_ipv6+0x1aa/0x1f0\n[...]\n\nImplement objref and objrefmap expression validate functions.\n\nCurrently, only NFT_OBJECT_SYNPROXY object type requires validation.\nThis will also handle a jump to a chain using a synproxy object from the\nOUTPUT hook.\n\nNow when trying to reference a synproxy object in the OUTPUT hook, nft\nwill produce the following error:\n\nsynproxy_crash.nft: Error: Could not process rule: Operation not supported\n synproxy name mysynproxy\n ^^^^^^^^^^^^^^^^^^^^^^^^"
}
],
"metrics": [
{
"cvssV3_1": {
"baseScore": 7.8,
"baseSeverity": "HIGH",
"vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H",
"version": "3.1"
},
"scenarios": [
{
"lang": "en",
"value": "AV:L - The flaw is enabled through an nftables ruleset installed over the NFNL_SUBSYS_NFTABLES netlink socket, and triggered by a locally-generated TCP SYN traversing the OUTPUT hook. Per netfilter/nftables convention this is a local attack surface, not a remotely reachable one.\nAC:L - Exploitation is fully deterministic \u2014 add a synproxy object reference to an OUTPUT base chain and emit any TCP SYN; there is no race, no memory-layout dependency, and no bound on the recursion depth. CONFIG_NFT_SYNPROXY is standard and autoloadable on distribution kernels.\nPR:L - nfnetlink_rcv checks netlink_net_capable(skb, CAP_NET_ADMIN), which evaluates against the network namespace\u0027s owning user namespace, so any unprivileged local user obtains it via `unshare -Urn`; nft_synproxy_do_init imposes no init_user_ns requirement. The resulting stack overflow is not confined to the namespace and takes down the host.\nUI:N - The attacker performs both steps \u2014 installing the rule and emitting the triggering SYN \u2014 with no action required from any other user or administrator.\nS:U - The recursion, the stack exhaustion, and the resulting panic all occur within the kernel\u0027s own security authority; no hypervisor, IOMMU, or other trust boundary is crossed.\nC:H - The unbounded recursion exhausts the kernel stack, and on the many embedded/IoT/automotive configurations lacking CONFIG_VMAP_STACK (arm32 without ARM_HAS_GROUP_RELOCS, and architectures with no VMAP_STACK support) it runs past the stack into adjacent kernel pages rather than into a guard page, corrupting neighbouring structures that can be leveraged for kernel memory disclosure.\nI:H - On those same non-VMAP_STACK configurations the overrun writes attacker-influenced frame contents \u2014 struct flowi6 built from the attacker\u0027s SYN addresses/ports, synproxy_options with attacker-chosen MSS/wscale/timestamps, and nft_regs \u2014 into adjacent kernel memory, and on architectures where thread_info sits at the stack base it clobbers that first, yielding an exploitable corruption primitive.\nA:H - The infinite recursion reliably exhausts the kernel stack and hits the guard page, producing an immediate kernel panic as shown in the reporter\u0027s trace. This is a complete denial of service triggerable at will by an unprivileged local user."
}
]
}
],
"providerMetadata": {
"dateUpdated": "2026-08-23T12:45:25.956Z",
"orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"shortName": "Linux"
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"url": "https://git.kernel.org/stable/c/0028e0134c64d9ed21728341a74fcfc59cd0f944"
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"url": "https://git.kernel.org/stable/c/7ea55a44493a5a36c3b3293b88bbe4841f9dbaf0"
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{
"url": "https://git.kernel.org/stable/c/4c1cf72ec10be5a9ad264650cadffa1fbce6fabd"
},
{
"url": "https://git.kernel.org/stable/c/f359b809d54c6e3dd1d039b97e0b68390b0e53e4"
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"title": "netfilter: nft_objref: validate objref and objrefmap expressions",
"x_generator": {
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"assignerShortName": "Linux",
"cveId": "CVE-2025-40206",
"datePublished": "2025-11-12T21:56:35.675Z",
"dateReserved": "2025-04-16T07:20:57.179Z",
"dateUpdated": "2026-08-23T12:45:25.956Z",
"state": "PUBLISHED"
},
"dataType": "CVE_RECORD",
"dataVersion": "5.2",
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"cve": "CVE-2025-40206",
"date": "2026-09-28",
"epss": "0.00142",
"percentile": "0.02926"
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"product": "Linux",
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"versions": [
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"cveTags": [],
"descriptions": [
{
"lang": "en",
"value": "In the Linux kernel, the following vulnerability has been resolved:\n\nnetfilter: nft_objref: validate objref and objrefmap expressions\n\nReferencing a synproxy stateful object from OUTPUT hook causes kernel\ncrash due to infinite recursive calls:\n\nBUG: TASK stack guard page was hit at 000000008bda5b8c (stack is 000000003ab1c4a5..00000000494d8b12)\n[...]\nCall Trace:\n __find_rr_leaf+0x99/0x230\n fib6_table_lookup+0x13b/0x2d0\n ip6_pol_route+0xa4/0x400\n fib6_rule_lookup+0x156/0x240\n ip6_route_output_flags+0xc6/0x150\n __nf_ip6_route+0x23/0x50\n synproxy_send_tcp_ipv6+0x106/0x200\n synproxy_send_client_synack_ipv6+0x1aa/0x1f0\n nft_synproxy_do_eval+0x263/0x310\n nft_do_chain+0x5a8/0x5f0 [nf_tables\n nft_do_chain_inet+0x98/0x110\n nf_hook_slow+0x43/0xc0\n __ip6_local_out+0xf0/0x170\n ip6_local_out+0x17/0x70\n synproxy_send_tcp_ipv6+0x1a2/0x200\n synproxy_send_client_synack_ipv6+0x1aa/0x1f0\n[...]\n\nImplement objref and objrefmap expression validate functions.\n\nCurrently, only NFT_OBJECT_SYNPROXY object type requires validation.\nThis will also handle a jump to a chain using a synproxy object from the\nOUTPUT hook.\n\nNow when trying to reference a synproxy object in the OUTPUT hook, nft\nwill produce the following error:\n\nsynproxy_crash.nft: Error: Could not process rule: Operation not supported\n synproxy name mysynproxy\n ^^^^^^^^^^^^^^^^^^^^^^^^"
}
],
"id": "CVE-2025-40206",
"lastModified": "2026-08-23T13:16:26.737",
"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"
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"impactScore": 5.9,
"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"type": "Secondary"
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"published": "2025-11-12T22:15:47.893",
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"url": "https://git.kernel.org/stable/c/0028e0134c64d9ed21728341a74fcfc59cd0f944"
},
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"url": "https://git.kernel.org/stable/c/4c1cf72ec10be5a9ad264650cadffa1fbce6fabd"
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}
],
"sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"vulnStatus": "Deferred"
}
},
"redhat_vex": {
"aggregate_severity": "Moderate",
"current_release_date": "2026-07-30T08:48:32+00:00",
"cve": "CVE-2025-40206",
"id": "CVE-2025-40206",
"initial_release_date": "2025-11-12T00:00:00+00:00",
"product_status:known_affected": "184",
"product_status:known_not_affected": "90",
"source": "Red Hat CSAF VEX",
"status": "final",
"title": "kernel: netfilter: nft_objref: validate objref and objrefmap expressions",
"url": "https://security.access.redhat.com/data/csaf/v2/vex/2025/cve-2025-40206.json",
"version": "3"
},
"suse_vex": {
"aggregate_severity": "moderate",
"current_release_date": "2026-09-19T02:06:10Z",
"cve": "CVE-2025-40206",
"id": "CVE-2025-40206",
"initial_release_date": "2025-11-14T00:23:41Z",
"product_status:first_fixed": "2",
"product_status:known_affected": "435",
"product_status:known_not_affected": "341",
"product_status:recommended": "464",
"source": "SUSE CSAF VEX",
"status": "interim",
"title": "SUSE CVE CVE-2025-40206",
"url": "https://ftp.suse.com/pub/projects/security/csaf-vex/cve-2025-40206.json",
"version": "37"
}
}
}
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Experimental. This forecast is provided for visualization only and may change without notice. Do not use it for operational decisions.
Forecast uses a logistic model when the trend is rising, or an exponential decay model when the trend is falling. Fitted via linearized least squares.
Sightings
| Author | Source | Type | Date | Other |
|---|
Nomenclature
- Seen: The vulnerability was mentioned, discussed, or observed by the user.
- Confirmed: The vulnerability has been validated from an analyst's perspective.
- Published Proof of Concept: A public proof of concept is available for this vulnerability.
- Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
- Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
- Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
- Not confirmed: The user expressed doubt about the validity of the vulnerability.
- Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.
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The MITRE ATT&CK techniques below are AI-generated suggestions, inferred from the description of the
vulnerability by the CIRCL/vulnerability-attack-technique-classification-roberta-base
model, served locally by ML-Gateway.
They have not been verified by an analyst and are provided for guidance only.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.
Browse all ATT&CK techniques and the vulnerabilities related to each.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.
Browse all ATT&CK techniques and the vulnerabilities related to each.
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Related by attack behaviour
Vulnerabilities whose description is nearest to this one in the vector space of the CIRCL/vulnerability-attack-technique-biencoder model. This is a similarity search over the bi-encoder space (plain cosine), not a classification, and it has no measured accuracy.
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