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CVE-2026-74563
rds: tcp: hold the RCU lock across ipv6_chk_addr() in rds_tcp_laddr_check()
Published 2026-08-15 (2 months ago) by the Linux kernel CNA. Subsystem net/rds. Debian urgency: not yet assigned.
What to do, per Debian release
Debian's own status for CVE-2026-74563 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-4777-1 · 2026-09-08 · text | 6.1.187-1 | Update the kernel and reboot. DLA-4777-1 shipped the fix on 2026-09-08, in 6.1.187-1. A running kernel keeps the old code until the machine restarts. |
| Debian 13trixie | fixedDSA-6466-1 · 2026-08-25 · text | 6.12.105-1 | Update the kernel and reboot. DSA-6466-1 shipped the fix on 2026-08-25, in 6.12.105-1. A running kernel keeps the old code until the machine restarts. |
| Debian 14forky | fixed | 7.1.8-1 | Update the kernel and reboot. Fixed in 7.1.8-1. A running kernel keeps the old code until the machine restarts. |
| Debian unstablesid | fixed | 7.1.8-1 | Update the kernel and reboot. Fixed in 7.1.8-1. A running kernel keeps the old code until the machine restarts. |
| Debian 12bookworm · linux-6.12 | fixedDLA-4788-1 · 2026-09-19 · text | 6.12.107-1~deb12u1 | Update the kernel and reboot. DLA-4788-1 shipped the fix on 2026-09-19, in 6.12.107-1~deb12u1. A running kernel keeps the old code until the machine restarts. |
The vulnerability
What the bug is
rds_tcp_laddr_check() looks up a scoped IPv6 interface with dev_get_by_index_rcu(), drops the RCU read-side lock, and only then passes the bare struct net_device * into ipv6_chk_addr(). dev_get_by_index_rcu() only keeps the device alive within the same RCU read-side section. After rcu_read_unlock(), a concurrent RTM_DELLINK can free the net_device; ipv6_chk_addr() then dereferences the stale pointer in __ipv6_chk_addr_and_flags() (e.g. l3mdev_master_dev_rcu(dev)), reading freed memory. Keep the RCU read-side lock held across the ipv6_chk_addr() call instead of dropping it right after the lookup, so the device cannot be freed while it is in use. BUG: KASAN: slab-use-after-free in __ipv6_chk_addr_and_flags (... net/ipv6/addrconf.c:1998) Read of size 8 at addr ffff8880106ec000 by task exploit/153 Call Trace: ... kasan_report (mm/kasan/report.c:595) __ipv6_chk_addr_and_flags (... net/ipv6/addrconf.c:1998) ipv6_chk_addr (net/ipv6/addrconf.c:2031 net/ipv6/addrconf.c:1972) rds_tcp_laddr_check (net/rds/tcp.c:370) rds_bind (net/rds/bind.c:248) __sys_bind (net/socket.c:1920) __x64_sys_bind (net/socket.c:1956) do_syscall_64 (arch/x86/entry/syscall_64.c:63) entry_SYSCALL_64_after_hwframe (arch/x86/entry/entry_64.S:121)
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.
net/rds/tcp.c
- What this is
- RDS - RELIABLE DATAGRAM SOCKETSMAINTAINERS section matched on net/rds/ · netdev@vger.kernel.org · Supported
- Kernel module
- rds_tcp
Check it on the machine
grep -wE 'CONFIG_RDS|CONFIG_RDS_TCP' /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.
lsmod | grep -w rds_tcpPrints a line if that module is loaded right now, and nothing if it is not. One that is not loaded can still be loaded later by anything that needs it.
Show whether Debian builds this, per release
Debian builds this as a loadable module. Every release below compiles it as a module on every flavour, so whether the code is in the running kernel depends on whether that module is loaded.
- bookworm, trixie, forky, sid, bookworm · linux-6.12m
- m
- a loadable module on every flavour - check lsmod, can be blacklisted
- Build switches
- CONFIG_RDS, CONFIG_RDS_TCP
- Reads as
- all on means the file is compiled; any one off means it is not.
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
- 2026-08-15 (2 months ago)source
- CVSS
- 7.8 high
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:Hsource recompute it - Attack vector
- local (AV:L)source
- EPSS
- 0.12%, higher than 1.6% of all CVEssource
- CISA KEV
- not listedthe KEV catalogue
- Debian urgency
- not yet assignedsource
- Subsystem
- net/rds
Upstream fixes
The versions the CNA records as introducing and fixing this, and the commit for each. source
| Introduced | Fixed in | Commit |
|---|---|---|
| 4.19 | 5.10.265 | f8a8977af213 |
| 4.19 | 5.15.216 | ba95bce5dfe6 |
| 4.19 | 6.1.183 | c4933624a6f4 |
| 4.19 | 6.6.151 | 76dd48886eee |
| 4.19 | 6.12.103 | f0d1fb05d70c |
| 4.19 | 6.18.44 | b1d480fce05f |
| 4.19 | 7.1.8 | 8398bc477d3c |
| 4.19 | 7.2 | 78f75d632f74 |
Debian advisories
| Advisory | Date | Shipped to | Debian |
|---|---|---|---|
| DLA-4788-1 | 2026-09-19 | bookworm 6.12.107-1~deb12u1 | tracker |
| DLA-4777-1 | 2026-09-08 | bookworm 6.1.187-1 | tracker |
| DSA-6466-1 | 2026-08-25 | trixie 6.12.105-1 | 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:LAttack vector, local
- The slab use-after-free is reached via the bind(2) syscall on an AF_RDS socket with a link-local IPv6 address and non-zero scope_id; the KASAN reproducer follows bind()->rds_bind()->rds_tcp_laddr_check(), requiring on-host access to race bind against RTM_DELLINK netlink deletion of the referenced netdev.
- AC:LAttack complexity, low
- Exploitation requires racing rds_tcp_laddr_check() against RTM_DELLINK freeing the netdev; the attacker controls both sides by concurrently calling bind() and deleting the interface via netlink (e.g., a veth in a user namespace) and can retry until the race succeeds.
- PR:LPrivileges required, low
- An unprivileged local user can create AF_RDS sockets and call bind(); the RTM_DELLINK race is achievable with CAP_NET_ADMIN obtainable inside an unprivileged user+network namespace (unshare -Urn), not requiring init-namespace root.
- UI:NUser interaction, none
- No victim interaction is required; exploitation is fully attacker-driven through bind/netlink syscalls without needing another user to mount a filesystem, click, or open a file.
- S:UScope, unchanged
- Impact is confined to kernel memory corruption and potential privilege escalation within the same kernel/host security boundary; this is not a VM-guest-to-host escape, sandbox escape, or cross-authority boundary crossing.
- C:HConfidentiality impact, high
- The bug is a slab use-after-free read of a freed struct net_device in __ipv6_chk_addr_and_flags() via a stale pointer passed to ipv6_chk_addr(); UAF reads of kernel heap objects can disclose sensitive memory and enable further exploitation.
- I:HIntegrity impact, high
- Use-after-free on struct net_device heap memory provides memory corruption primitives that can be groomed for arbitrary kernel writes, control-flow hijacking, and local privilege escalation, not merely a bounded or transient error.
- A:HAvailability impact, high
- The reported KASAN slab-use-after-free causes kernel oops/panic during the stale dereference in the IPv6 address-check path; UAF conditions are inherently crash-prone even when not fully weaponized for code execution.