GHSA-CF89-F375-P3PC
Vulnerability from github – Published: 2026-09-17 18:31 – Updated: 2026-09-18 18:31In the Linux kernel, the following vulnerability has been resolved:
inetpeer: randomize RB-tree node comparison using SipHash
The inetpeer rate limiting system stores peer entries in a Red-Black tree keyed deterministically on the remote IP address. Because tree lookups walk the RB-tree using standard lexicographical comparisons (inetpeer_addr_cmp), an off-path adversary can predict the exact topology of the tree and the sequence of nodes traversed during lookups (the gc_stack candidate list).
By combining deterministic tree traversal with aggressive garbage collection (triggered when tree size exceeds inet_peer_threshold), an attacker can selectively force the eviction of targeted inet_peer nodes. When an evicted node is subsequently re-created upon receiving a new packet, its rate-limiting token bucket (rate_tokens, rate_last) is reset to full capacity. This creates a side-channel primitive allowing off-path attackers to bypass IP-keyed ICMP rate limits and infer open UDP ports (similar to SAD DNS style attacks).
Mitigate this by randomizing the RB-tree node comparison logic using SipHash with a secret key (inetpeer_hash_key) initialized via net_get_random_once(). Nodes are ordered in the tree by SipHash(addr, key) rather than raw IP addresses. Because the secret key is unknown to external entities, the tree layout and lookup traversal paths are unpredictable to off-path adversaries, breaking the deterministic eviction gadget.
Cache the computed 64-bit SipHash (hash) in struct inet_peer and compute the target hash (dhash) once at the beginning of inet_getpeer() to avoid recomputing SipHash at every step of the RB-tree walk.
{
"affected": [],
"aliases": [
"CVE-2026-90110"
],
"database_specific": {
"cwe_ids": [],
"github_reviewed": false,
"github_reviewed_at": null,
"nvd_published_at": "2026-09-17T17:17:02Z",
"severity": "CRITICAL"
},
"details": "In the Linux kernel, the following vulnerability has been resolved:\n\ninetpeer: randomize RB-tree node comparison using SipHash\n\nThe inetpeer rate limiting system stores peer entries in a Red-Black tree\nkeyed deterministically on the remote IP address. Because tree lookups walk\nthe RB-tree using standard lexicographical comparisons (inetpeer_addr_cmp),\nan off-path adversary can predict the exact topology of the tree and the\nsequence of nodes traversed during lookups (the gc_stack candidate list).\n\nBy combining deterministic tree traversal with aggressive garbage collection\n(triggered when tree size exceeds inet_peer_threshold), an attacker can\nselectively force the eviction of targeted inet_peer nodes. When an evicted\nnode is subsequently re-created upon receiving a new packet, its rate-limiting\ntoken bucket (rate_tokens, rate_last) is reset to full capacity. This creates\na side-channel primitive allowing off-path attackers to bypass IP-keyed ICMP\nrate limits and infer open UDP ports (similar to SAD DNS style attacks).\n\nMitigate this by randomizing the RB-tree node comparison logic using SipHash\nwith a secret key (inetpeer_hash_key) initialized via net_get_random_once().\nNodes are ordered in the tree by SipHash(addr, key) rather than raw IP\naddresses. Because the secret key is unknown to external entities, the tree\nlayout and lookup traversal paths are unpredictable to off-path adversaries,\nbreaking the deterministic eviction gadget.\n\nCache the computed 64-bit SipHash (hash) in struct inet_peer and compute the\ntarget hash (dhash) once at the beginning of inet_getpeer() to avoid recomputing\nSipHash at every step of the RB-tree walk.",
"id": "GHSA-cf89-f375-p3pc",
"modified": "2026-09-18T18:31:27Z",
"published": "2026-09-17T18:31:51Z",
"references": [
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2026-90110"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/199fcf285e498111e029137d088949bc6c26d578"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/2ee66e9487172fcd189bc52a767c30dad7141c09"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/5f127e3cc9647a8a70db12c65dbd0de473545380"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/7109bb63667a53e4542ad845476f97d0c8b28a61"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/857681f6835d5b0a7bc4a34a026baeaaf5215623"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/b20e98f0bb668a59abaf7bcf85d75c073e90d352"
}
],
"schema_version": "1.4.0",
"severity": [
{
"score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:L",
"type": "CVSS_V3"
}
]
}
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