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CVE-2026-90110
inetpeer: randomize RB-tree node comparison using SipHash
Published 2026-09-17 (31 days ago) by the Linux kernel CNA. Subsystem include/net. Debian urgency: not yet assigned.
What to do, per Debian release
Debian's own status for CVE-2026-90110 in every release this site tracks, and what each one means in practice. Every status below is the one the Debian Security Team publishes for this CVE. source
| Release | Status | Version | What this means |
|---|---|---|---|
| Debian 12bookworm | fixedDLA-4841-1 · 2026-10-17 · text | 6.1.190-1 | Update the kernel and reboot. DLA-4841-1 shipped the fix on 2026-10-17, in 6.1.190-1. A running kernel keeps the old code until the machine restarts. |
| Debian 13trixie | fixedDSA-6528-1 · 2026-09-29 · text | 6.12.111-1 | Update the kernel and reboot. DSA-6528-1 shipped the fix on 2026-09-29, in 6.12.111-1. A running kernel keeps the old code until the machine restarts. |
| Debian 14forky | fixed | 7.2.6-1 | Update the kernel and reboot. Fixed in 7.2.6-1. A running kernel keeps the old code until the machine restarts. |
| Debian unstablesid | fixed | 7.2.6-1 | Update the kernel and reboot. Fixed in 7.2.6-1. A running kernel keeps the old code until the machine restarts. |
| Debian 12bookworm · linux-6.12 | fixedDLA-4817-1 · 2026-10-04 · text | 6.12.111-1~deb12u1 | Update the kernel and reboot. DLA-4817-1 shipped the fix on 2026-10-04, in 6.12.111-1~deb12u1. A running kernel keeps the old code until the machine restarts. |
The vulnerability
What the bug is
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.
Where it lives
The fix touches these files. If the subsystem is one you do not use, the practical exposure is lower, though the package is still the vulnerable one.
include/net/inetpeer.h
net/ipv4/inetpeer.c
- What this is
- NETWORKING [IPv4/IPv6]MAINTAINERS section matched on include/net/inetpeer.h · netdev@vger.kernel.org · Maintained
Check it on the machine
grep -w CONFIG_INET /boot/config-$(uname -r)Reads the booted kernel's own configuration, on the machine and nowhere else. =y is built in, =m is a module, and an is not set line means the code is not there.
Show whether Debian builds this, per release
Debian builds this code. Every release below compiles the affected file into the kernels it ships.
- bookworm, trixie, forky, sid, bookworm · linux-6.12y
- y
- built into the kernel image on every flavour - only a patch removes it
- Build switch
- CONFIG_INET
From the configuration Debian publishes for every kernel flavour it builds. It covers only the architectures Debian ships a linux-config package for, and nothing about a kernel you built yourself. Debian's own status above stays authoritative about the source package.MAINTAINERS kbuild Makefiles Debian linux-config packages
Signals
- Published
- 2026-09-17 (31 days ago)source
- CVSS
- 9.4 critical
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:Lsource recompute it - Attack vector
- network (AV:N)source
- EPSS
- 0.61%, higher than 48.2% of all CVEssource
- CISA KEV
- not listedthe KEV catalogue
- Debian urgency
- not yet assignedsource
- Subsystem
- include/net
Upstream fixes
The versions the CNA records as introducing and fixing this, and the commit for each. source
| Introduced | Fixed in | Commit |
|---|---|---|
| 4.14 | 6.1.188 | b20e98f0bb66 |
| 4.14 | 6.6.157 | 5f127e3cc964 |
| 4.14 | 6.12.110 | 199fcf285e49 |
| 4.14 | 6.18.52 | 857681f6835d |
| 4.14 | 7.2.6 | 7109bb63667a |
| 4.14 | 7.3 | 2ee66e948717 |
Debian advisories
| Advisory | Date | Shipped to | Debian |
|---|---|---|---|
| DLA-4841-1 | 2026-10-17 | bookworm 6.1.190-1 | tracker |
| DLA-4817-1 | 2026-10-04 | bookworm 6.12.111-1~deb12u1 | tracker |
| DSA-6528-1 | 2026-09-29 | trixie 6.12.111-1 | tracker |
Why the CNA scored it this way
Quoted from the kernel CNA's own scoring file, word for word. A highlighted metric carries the most severe value CVSS v3.1 defines for it, which is what pushes the score up. source
- AV:NAttack vector, network
- A received IPv4 UDP datagram to a closed port takes ip_rcv → ip_local_deliver → udp_rcv() → icmp_send() → icmpv4_xrlim_allow() → inet_getpeer_v4(), with icmp_route_lookup() setting fl4->daddr from iph->saddr; ip4_frag_init() also keys inet_getpeer_v4() on the fragment source. Those attacker-chosen addresses are the inetpeer RB-tree keys on a routable IP path.
- AC:LAttack complexity, low
- The attacker chooses the source addresses inetpeer_addr_cmp() orders, grows base->total past inet_peer_threshold via inet_getpeer() on those UDP/ICMP or fragment lookups, then looks up further keys so lookup() pushes the victim inet_peer onto gc_stack and inet_peer_gc() evicts it (ttl=0, refcount_dec_if_one). Tree shape and eviction set are functions of those keys, not uninfluenced victim state.
- PR:NPrivileges required, none
- udp_rcv() emits ICMP_PORT_UNREACH and icmpv4_xrlim_allow() calls inet_getpeer_v4() for any inbound IPv4/UDP packet with no socket, credential, or capability check; ip4_frag_init() likewise creates peers from unauthenticated fragment sources.
- UI:NUser interaction, none
- Peer insertion in inet_getpeer(), gc_stack collection in lookup(), and the rate_tokens/rate_last reset when a GC'd inet_peer is kmem_cache_alloc'd again all run in the receive/softirq path of the attacker's own packets; no local user must mount, open, or otherwise act.
- S:UScope, unchanged
- The inet_peer RB-tree and ICMP token bucket live in the host IPv4/IPv6 stack; any recovered UDP port or poisoned resolver cache remains that host's network-stack authority, with no VM, IOMMU, or sandbox boundary crossed.
- C:HConfidentiality impact, high
- Evicting a chosen node via lookup()'s gc_stack and recreating it in inet_getpeer() sets rate_tokens=0 and rate_last=jiffies-60*HZ so inet_peer_xrlim_allow() starts at full burst, resetting the per-IP ICMP oracle and letting an off-path attacker infer open/ephemeral UDP ports (SAD DNS), defeating source-port randomization.
- I:HIntegrity impact, high
- Recovering the ephemeral UDP source port of an in-flight DNS query through that reset inet_peer_xrlim_allow() oracle lets the same off-path attacker spoof the nameserver reply, win the race against the legitimate response, and poison the resolver cache, arbitrarily redirecting later lookups.
- A:LAvailability impact, low
- Repeated inet_peer_gc() eviction and inet_getpeer() recreate of rate_tokens lets the attacker keep passing inet_peer_xrlim_allow() and drain icmp_global_credit, suppressing ICMP errors (port unreachable, time exceeded) to other peers; lookup() and inet_peer_gc() do not oops, so the loss is ICMP signalling degradation rather than a crash.