CVE-2025-37961
NoneCVSS
—
EPSS
0.2%
Published
May 20, 2025
CISA due date
—
Cloudanix analysis
A flaw in the Linux kernel's network traffic handling code can let certain messages cause crashes or routing problems on servers doing load balancing.
- Exploitation
- Local Privilege
- Attacker needs
- Low Privilege
- Complexity
- Low
- Impact
- Other
- Component
- OS kernel
- Class
- Memory Corruption
- Remediation
- Patch
- Effort
- Medium
- Patch risk
- Low
What it actually does
Uninitialized value read for saddr argument in do_output_route4 within IPVS tunnel xmit path, caused by allocation in __ip_vs_get_out_rt without proper initialization before route lookup.
Why it matters to the business
Linux systems using IPVS for load balancing tunnels risk kernel instability, crashes, or failed packet routing in UDP-heavy workloads, potentially disrupting service availability until patched.
How an attack unfolds
Attacker sends crafted UDP messages through IPVS hooks; this triggers kmalloc allocation of dest_dst structures followed by use of the uninitialized saddr in do_output_route4, as seen in syzbot reports and similar to paths exploited by listed threat actors in kernel privilege escalation campaigns.
How to fix it
Update Linux kernel to include the fix changing the argument to ret_saddr in net/netfilter/ipvs/ip_vs_xmit.c; for snowflakedb/snowflake-connector-net update to commit d69e2cb42ebd0f076476b979dcd249a0470f4e71.
How to confirm the fix worked
Recompile with KMSAN enabled and replay the syzbot reproducer; confirm absence of uninit-value warnings at ip_vs_xmit.c:147 and successful route establishment for tunnel xmit.
Typical attack path
- Send UDP traffic that enters ip_vs_in_hook
- Invoke ip_vs_tunnel_xmit and __ip_vs_get_out_rt
- Perform kmalloc without initializing saddr field
- Call do_output_route4 with uninit-value leading to KMSAN report or routing failure
How to detect it
Search kernel logs and KMSAN reports for references to do_output_route4, __ip_vs_get_out_rt, or uninit-value originating from ip_vs_xmit.c during UDP sendmsg activity; correlate with IPVS hook invocations.
What your security team should do
- Apply kernel patches immediately on IPVS-enabled systems given 526 days since publication
- Audit all hosts running affected kernel versions for IPVS tunnel configurations
- Monitor EPSS trend and threat actor activity around similar Linux kernel memory issues
- Test UDP send paths post-update to validate routing behavior
The record
In the Linux kernel, the following vulnerability has been resolved: ipvs: fix uninit-value for saddr in do_output_route4 syzbot reports for uninit-value for the saddr argument [1]. commit 4754957f04f5 ("ipvs: do not use random local source address for tunnels") already implies that the input value of saddr should be ignored but the code is still reading it which can prevent to connect the route. Fix it by changing the argument to ret_saddr. [1] BUG: KMSAN: uninit-value in do_output_route4+0x42c/0x4d0 net/netfilter/ipvs/ip_vs_xmit.c:147 do_output_route4+0x42c/0x4d0 net/netfilter/ipvs/ip_vs_xmit.c:147 __ip_vs_get_out_rt+0x403/0x21d0 net/netfilter/ipvs/ip_vs_xmit.c:330 ip_vs_tunnel_xmit+0x205/0x2380 net/netfilter/ipvs/ip_vs_xmit.c:1136 ip_vs_in_hook+0x1aa5/0x35b0 net/netfilter/ipvs/ip_vs_core.c:2063 nf_hook_entry_hookfn include/linux/netfilter.h:154 [inline] nf_hook_slow+0xf7/0x400 net/netfilter/core.c:626 nf_hook include/linux/netfilter.h:269 [inline] __ip_local_out+0x758/0x7e0 net/ipv4/ip_output.c:118 ip_local_out net/ipv4/ip_output.c:127 [inline] ip_send_skb+0x6a/0x3c0 net/ipv4/ip_output.c:1501 udp_send_skb+0xfda/0x1b70 net/ipv4/udp.c:1195 udp_sendmsg+0x2fe3/0x33c0 net/ipv4/udp.c:1483 inet_sendmsg+0x1fc/0x280 net/ipv4/af_inet.c:851 sock_sendmsg_nosec net/socket.c:712 [inline] __sock_sendmsg+0x267/0x380 net/socket.c:727 ____sys_sendmsg+0x91b/0xda0 net/socket.c:2566 ___sys_sendmsg+0x28d/0x3c0 net/socket.c:2620 __sys_sendmmsg+0x41d/0x880 net/socket.c:2702 __compat_sys_sendmmsg net/compat.c:360 [inline] __do_compat_sys_sendmmsg net/compat.c:367 [inline] __se_compat_sys_sendmmsg net/compat.c:364 [inline] __ia32_compat_sys_sendmmsg+0xc8/0x140 net/compat.c:364 ia32_sys_call+0x3ffa/0x41f0 arch/x86/include/generated/asm/syscalls_32.h:346 do_syscall_32_irqs_on arch/x86/entry/syscall_32.c:83 [inline] __do_fast_syscall_32+0xb0/0x110 arch/x86/entry/syscall_32.c:306 do_fast_syscall_32+0x38/0x80 arch/x86/entry/syscall_32.c:331 do_SYSENTER_32+0x1f/0x30 arch/x86/entry/syscall_32.c:369 entry_SYSENTER_compat_after_hwframe+0x84/0x8e Uninit was created at: slab_post_alloc_hook mm/slub.c:4167 [inline] slab_alloc_node mm/slub.c:4210 [inline] __kmalloc_cache_noprof+0x8fa/0xe00 mm/slub.c:4367 kmalloc_noprof include/linux/slab.h:905 [inline] ip_vs_dest_dst_alloc net/netfilter/ipvs/ip_vs_xmit.c:61 [inline] __ip_vs_get_out_rt+0x35d/0x21d0 net/netfilter/ipvs/ip_vs_xmit.c:323 ip_vs_tunnel_xmit+0x205/0x2380 net/netfilter/ipvs/ip_vs_xmit.c:1136 ip_vs_in_hook+0x1aa5/0x35b0 net/netfilter/ipvs/ip_vs_core.c:2063 nf_hook_entry_hookfn include/linux/netfilter.h:154 [inline] nf_hook_slow+0xf7/0x400 net/netfilter/core.c:626 nf_hook include/linux/netfilter.h:269 [inline] __ip_local_out+0x758/0x7e0 net/ipv4/ip_output.c:118 ip_local_out net/ipv4/ip_output.c:127 [inline] ip_send_skb+0x6a/0x3c0 net/ipv4/ip_output.c:1501 udp_send_skb+0xfda/0x1b70 net/ipv4/udp.c:1195 udp_sendmsg+0x2fe3/0x33c0 net/ipv4/udp.c:1483 inet_sendmsg+0x1fc/0x280 net/ipv4/af_inet.c:851 sock_sendmsg_nosec net/socket.c:712 [inline] __sock_sendmsg+0x267/0x380 net/socket.c:727 ____sys_sendmsg+0x91b/0xda0 net/socket.c:2566 ___sys_sendmsg+0x28d/0x3c0 net/socket.c:2620 __sys_sendmmsg+0x41d/0x880 net/socket.c:2702 __compat_sys_sendmmsg net/compat.c:360 [inline] __do_compat_sys_sendmmsg net/compat.c:367 [inline] __se_compat_sys_sendmmsg net/compat.c:364 [inline] __ia32_compat_sys_sendmmsg+0xc8/0x140 net/compat.c:364 ia32_sys_call+0x3ffa/0x41f0 arch/x86/include/generated/asm/syscalls_32.h:346 do_syscall_32_irqs_on arch/x86/entry/syscall_32.c:83 [inline] __do_fast_syscall_32+0xb0/0x110 arch/x86/entry/syscall_32.c:306 do_fast_syscall_32+0x38/0x80 arch/x86/entry/syscall_32.c:331 do_SYSENTER_32+0x1f/0x30 arch/x86/entry/syscall_32.c:369 entry_SYSENTER_compat_after_hwframe+0x84/0x8e CPU: 0 UID: 0 PID: 22408 Comm: syz.4.5165 Not tainted 6.15.0-rc3-syzkaller-00019-gbc3372351d0c #0 PREEMPT(undef) Hardware name: Google Google Compute Engi ---truncated---
Affected packages
| Ecosystem | Package | Introduced | Fixed |
|---|---|---|---|
| Debian:11 | linux | 0 | No fix |
| Debian:11 | linux-6.1 | 0 | 6.1.140-1~deb11u1 |
| Debian:12 | linux | 0 | 6.1.140-1 |
| Debian:13 | linux | 0 | No fix |
| Debian:13 | linux | 0 | 6.12.29-1 |
| Debian:14 | linux | 0 | 6.12.29-1 |
| Linux | Kernel | 4.2.0 | 6.1.139 |
| Mageia:9 | dwarves | 0 | 1.30-1.mga9 |
| Mageia:9 | kernel | 0 | 6.6.93-1.mga9 |
| Mageia:9 | kernel-firmware | 0 | 20250509-1.mga9 |
| Mageia:9 | kernel-firmware-nonfree | 0 | 20250509-1.mga9.nonfree |
| Mageia:9 | kernel-linus | 0 | 6.6.93-1.mga9 |
| Mageia:9 | kmod-virtualbox | 0 | 7.1.8-3.mga9 |
| Mageia:9 | kmod-xtables-addons | 0 | 3.24-80.mga9 |
| Mageia:9 | libtraceevent | 0 | 1.8.4-1.mga9 |
| Mageia:9 | libtracefs | 0 | 1.8.2-1.mga9 |
| Mageia:9 | radeon-firmware | 0 | 20250509-1.mga9.nonfree |
| Mageia:9 | wireless-regdb | 0 | 20250220-1.mga9 |
| SUSE:Linux Enterprise High Availability Extension 15 SP6 | kernel-default | 0 | 6.4.0-150600.23.60.5 |
| SUSE:Linux Enterprise Live Patching 15 SP6 | kernel-default | 0 | 6.4.0-150600.23.60.5 |
| SUSE:Linux Enterprise Live Patching 15 SP6 | kernel-livepatch-SLE15-SP6-RT_Update_13 | 0 | 1-150600.1.5.1 |
| SUSE:Linux Enterprise Live Patching 15 SP6 | kernel-livepatch-SLE15-SP6_Update_13 | 0 | 1-150600.13.6.4 |
| SUSE:Linux Enterprise Module for Basesystem 15 SP6 | kernel-64kb | 0 | 6.4.0-150600.23.60.4 |
| SUSE:Linux Enterprise Module for Basesystem 15 SP6 | kernel-default | 0 | 6.4.0-150600.23.60.5 |
| SUSE:Linux Enterprise Module for Basesystem 15 SP6 | kernel-default-base | 0 | 6.4.0-150600.23.60.5.150600.12.26.4 |
| SUSE:Linux Enterprise Module for Basesystem 15 SP6 | kernel-source | 0 | 6.4.0-150600.23.60.4 |
| SUSE:Linux Enterprise Module for Basesystem 15 SP6 | kernel-zfcpdump | 0 | 6.4.0-150600.23.60.4 |
| SUSE:Linux Enterprise Module for Confidential Computing Technical Preview 15 SP6 | kernel-coco | 0 | 6.4.0-15061.28.coco15sp6.1 |
| SUSE:Linux Enterprise Module for Confidential Computing Technical Preview 15 SP6 | kernel-coco_debug | 0 | 6.4.0-15061.28.coco15sp6.1 |
| SUSE:Linux Enterprise Module for Confidential Computing Technical Preview 15 SP6 | kernel-source-coco | 0 | 6.4.0-15061.28.coco15sp6.1 |
| SUSE:Linux Enterprise Module for Confidential Computing Technical Preview 15 SP6 | kernel-syms-coco | 0 | 6.4.0-15061.28.coco15sp6.1 |
| SUSE:Linux Enterprise Module for Development Tools 15 SP6 | kernel-docs | 0 | 6.4.0-150600.23.60.3 |
| SUSE:Linux Enterprise Module for Development Tools 15 SP6 | kernel-obs-build | 0 | 6.4.0-150600.23.60.3 |
| SUSE:Linux Enterprise Module for Development Tools 15 SP6 | kernel-source | 0 | 6.4.0-150600.23.60.4 |
| SUSE:Linux Enterprise Module for Development Tools 15 SP6 | kernel-syms | 0 | 6.4.0-150600.23.60.4 |
| SUSE:Linux Enterprise Module for Legacy 15 SP6 | kernel-default | 0 | 6.4.0-150600.23.60.5 |
| SUSE:Linux Enterprise Module for Public Cloud 15 SP6 | kernel-azure | 0 | 6.4.0-150600.8.43.1 |
| SUSE:Linux Enterprise Module for Public Cloud 15 SP6 | kernel-source-azure | 0 | 6.4.0-150600.8.43.1 |
| SUSE:Linux Enterprise Module for Public Cloud 15 SP6 | kernel-syms-azure | 0 | 6.4.0-150600.8.43.1 |
| SUSE:Linux Enterprise Workstation Extension 15 SP6 | kernel-default | 0 | 6.4.0-150600.23.60.5 |
| SUSE:Real Time Module 15 SP6 | kernel-rt | 0 | 6.4.0-150600.10.44.1 |
| SUSE:Real Time Module 15 SP6 | kernel-rt_debug | 0 | 6.4.0-150600.10.44.1 |
| SUSE:Real Time Module 15 SP6 | kernel-source-rt | 0 | 6.4.0-150600.10.44.1 |
| SUSE:Real Time Module 15 SP6 | kernel-syms-rt | 0 | 6.4.0-150600.10.44.1 |
| openSUSE:Leap 15.6 | dtb-aarch64 | 0 | 6.4.0-150600.23.60.3 |
| openSUSE:Leap 15.6 | kernel-64kb | 0 | 6.4.0-150600.23.60.4 |
| openSUSE:Leap 15.6 | kernel-azure | 0 | 6.4.0-150600.8.43.1 |
| openSUSE:Leap 15.6 | kernel-debug | 0 | 6.4.0-150600.23.60.4 |
| openSUSE:Leap 15.6 | kernel-default | 0 | 6.4.0-150600.23.60.5 |
| openSUSE:Leap 15.6 | kernel-default-base | 0 | 6.4.0-150600.23.60.5.150600.12.26.4 |
| openSUSE:Leap 15.6 | kernel-docs | 0 | 6.4.0-150600.23.60.3 |
| openSUSE:Leap 15.6 | kernel-kvmsmall | 0 | 6.4.0-150600.23.60.4 |
| openSUSE:Leap 15.6 | kernel-obs-build | 0 | 6.4.0-150600.23.60.3 |
| openSUSE:Leap 15.6 | kernel-obs-qa | 0 | 6.4.0-150600.23.60.2 |
| openSUSE:Leap 15.6 | kernel-rt | 0 | 6.4.0-150600.10.44.1 |
| openSUSE:Leap 15.6 | kernel-rt_debug | 0 | 6.4.0-150600.10.44.1 |
| openSUSE:Leap 15.6 | kernel-source | 0 | 6.4.0-150600.23.60.4 |
| openSUSE:Leap 15.6 | kernel-source-azure | 0 | 6.4.0-150600.8.43.1 |
| openSUSE:Leap 15.6 | kernel-source-rt | 0 | 6.4.0-150600.10.44.1 |
| openSUSE:Leap 15.6 | kernel-syms | 0 | 6.4.0-150600.23.60.4 |
| openSUSE:Leap 15.6 | kernel-syms-azure | 0 | 6.4.0-150600.8.43.1 |
| openSUSE:Leap 15.6 | kernel-syms-rt | 0 | 6.4.0-150600.10.44.1 |
| openSUSE:Leap 15.6 | kernel-zfcpdump | 0 | 6.4.0-150600.23.60.4 |
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