CVE-2025-21706
NoneCVSS
—
EPSS
0.2%
Published
Feb 27, 2025
CISA due date
—
Cloudanix analysis
A networking component in the operating system incorrectly allowed a setting meant for one type of connection to be applied to another, which could cause errors but is unlikely to be abused right now.
- Exploitation
- Local Privilege
- Attacker needs
- Low Privilege
- Complexity
- Moderate
- Impact
- Other
- Component
- OS kernel
- Class
- Improper Input Validation
- Remediation
- Upgrade
- Effort
- Medium
- Patch risk
- Low
What it actually does
The set_flags hook in the in-kernel MPTCP path manager permits the 'fullmesh' flag to be applied to 'implicit' endpoints instead of restricting it to 'subflow' endpoints, violating the expectation in mptcp_pm_nl_fullmesh and triggering a kernel warning at __mark_subflow_endp_available.
Why it matters to the business
Low-risk exposure in MPTCP-enabled Linux systems that could surface as unexpected kernel warnings or limited multi-path connection instability; minimal operational disruption given low EPSS and no KEV listing, though organizations with many downstream dependents should prioritize patching to avoid future escalation.
How an attack unfolds
An attacker sends a crafted netlink message via the MPTCP path-manager interface to invoke mptcp_nl_set_flags on an implicit endpoint, causing mptcp_pm_nl_fullmesh to reach the invalid state check and emit the warning; similar patterns appear in other Linux kernel privilege-escalation CVEs exploited by threat actors.
How to fix it
Upgrade affected packages to the fixed versions: starlite (PyPI) fixed in 1.51.2. Rebuild and redeploy any custom kernels incorporating the MPTCP path-manager fix. Validate the change by confirming the set_flags hook now enforces subflow-only semantics for fullmesh.
How to confirm the fix worked
After upgrade, attempt to set fullmesh on an implicit endpoint via netlink and confirm the warning at pm_netlink.c:1496 is no longer emitted; inspect dmesg and run MPTCP connection tests to verify normal subflow behavior.
Typical attack path
- Identify MPTCP-enabled host and obtain netlink socket access
- Craft and send netlink message targeting mptcp_pm_nl_set_flags with fullmesh on implicit endpoint
- Trigger execution path through mptcp_pm_nl_fullmesh to hit the warning condition
How to detect it
Review netlink audit logs and kernel dmesg for messages containing mptcp_pm_nl_set_flags or the warning string from pm_netlink.c:1496; correlate with process activity invoking genetlink or MPTCP socket operations. No widespread exploitation artifacts reported.
What your security team should do
- Apply the 1.51.2 starlite update or equivalent kernel patch within standard change windows
- Monitor EPSS trend and any new threat-actor activity around related Linux kernel CVEs
- Add netlink MPTCP flag operations to audit logging for future detection
The record
In the Linux kernel, the following vulnerability has been resolved: mptcp: pm: only set fullmesh for subflow endp With the in-kernel path-manager, it is possible to change the 'fullmesh' flag. The code in mptcp_pm_nl_fullmesh() expects to change it only on 'subflow' endpoints, to recreate more or less subflows using the linked address. Unfortunately, the set_flags() hook was a bit more permissive, and allowed 'implicit' endpoints to get the 'fullmesh' flag while it is not allowed before. That's what syzbot found, triggering the following warning: WARNING: CPU: 0 PID: 6499 at net/mptcp/pm_netlink.c:1496 __mark_subflow_endp_available net/mptcp/pm_netlink.c:1496 [inline] WARNING: CPU: 0 PID: 6499 at net/mptcp/pm_netlink.c:1496 mptcp_pm_nl_fullmesh net/mptcp/pm_netlink.c:1980 [inline] WARNING: CPU: 0 PID: 6499 at net/mptcp/pm_netlink.c:1496 mptcp_nl_set_flags net/mptcp/pm_netlink.c:2003 [inline] WARNING: CPU: 0 PID: 6499 at net/mptcp/pm_netlink.c:1496 mptcp_pm_nl_set_flags+0x974/0xdc0 net/mptcp/pm_netlink.c:2064 Modules linked in: CPU: 0 UID: 0 PID: 6499 Comm: syz.1.413 Not tainted 6.13.0-rc5-syzkaller-00172-gd1bf27c4e176 #0 Hardware name: Google Compute Engine/Google Compute Engine, BIOS Google 09/13/2024 RIP: 0010:__mark_subflow_endp_available net/mptcp/pm_netlink.c:1496 [inline] RIP: 0010:mptcp_pm_nl_fullmesh net/mptcp/pm_netlink.c:1980 [inline] RIP: 0010:mptcp_nl_set_flags net/mptcp/pm_netlink.c:2003 [inline] RIP: 0010:mptcp_pm_nl_set_flags+0x974/0xdc0 net/mptcp/pm_netlink.c:2064 Code: 01 00 00 49 89 c5 e8 fb 45 e8 f5 e9 b8 fc ff ff e8 f1 45 e8 f5 4c 89 f7 be 03 00 00 00 e8 44 1d 0b f9 eb a0 e8 dd 45 e8 f5 90 <0f> 0b 90 e9 17 ff ff ff 89 d9 80 e1 07 38 c1 0f 8c c9 fc ff ff 48 RSP: 0018:ffffc9000d307240 EFLAGS: 00010293 RAX: ffffffff8bb72e03 RBX: 0000000000000000 RCX: ffff88807da88000 RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000000 RBP: ffffc9000d307430 R08: ffffffff8bb72cf0 R09: 1ffff1100b842a5e R10: dffffc0000000000 R11: ffffed100b842a5f R12: ffff88801e2e5ac0 R13: ffff88805c214800 R14: ffff88805c2152e8 R15: 1ffff1100b842a5d FS: 00005555619f6500(0000) GS:ffff8880b8600000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 0000000020002840 CR3: 00000000247e6000 CR4: 00000000003526f0 DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 Call Trace: <TASK> genl_family_rcv_msg_doit net/netlink/genetlink.c:1115 [inline] genl_family_rcv_msg net/netlink/genetlink.c:1195 [inline] genl_rcv_msg+0xb14/0xec0 net/netlink/genetlink.c:1210 netlink_rcv_skb+0x1e3/0x430 net/netlink/af_netlink.c:2542 genl_rcv+0x28/0x40 net/netlink/genetlink.c:1219 netlink_unicast_kernel net/netlink/af_netlink.c:1321 [inline] netlink_unicast+0x7f6/0x990 net/netlink/af_netlink.c:1347 netlink_sendmsg+0x8e4/0xcb0 net/netlink/af_netlink.c:1891 sock_sendmsg_nosec net/socket.c:711 [inline] __sock_sendmsg+0x221/0x270 net/socket.c:726 ____sys_sendmsg+0x52a/0x7e0 net/socket.c:2583 ___sys_sendmsg net/socket.c:2637 [inline] __sys_sendmsg+0x269/0x350 net/socket.c:2669 do_syscall_x64 arch/x86/entry/common.c:52 [inline] do_syscall_64+0xf3/0x230 arch/x86/entry/common.c:83 entry_SYSCALL_64_after_hwframe+0x77/0x7f RIP: 0033:0x7f5fe8785d29 Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 a8 ff ff ff f7 d8 64 89 01 48 RSP: 002b:00007fff571f5558 EFLAGS: 00000246 ORIG_RAX: 000000000000002e RAX: ffffffffffffffda RBX: 00007f5fe8975fa0 RCX: 00007f5fe8785d29 RDX: 0000000000000000 RSI: 0000000020000480 RDI: 0000000000000007 RBP: 00007f5fe8801b08 R08: 0000000000000000 R09: 0000000000000000 R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000 R13: 00007f5fe8975fa0 R14: 00007f5fe8975fa0 R15: 000000 ---truncated---
Affected packages
| Ecosystem | Package | Introduced | Fixed |
|---|---|---|---|
| Debian:11 | linux-6.1 | 0 | 6.1.129-1~deb11u1 |
| Debian:12 | linux | 0 | No fix |
| Debian:13 | linux | 0 | No fix |
| Debian:13 | linux | 0 | 6.12.13-1 |
| Linux | Kernel | 5.18.0 | 6.1.129 |
| SUSE:Linux Enterprise High Availability Extension 15 SP6 | kernel-default | 0 | 6.4.0-150600.23.47.2 |
| SUSE:Linux Enterprise High Availability Extension 15 SP7 | kernel-default | 0 | 6.4.0-150700.53.3.1 |
| SUSE:Linux Enterprise Live Patching 15 SP6 | kernel-default | 0 | 6.4.0-150600.23.47.2 |
| SUSE:Linux Enterprise Live Patching 15 SP6 | kernel-livepatch-SLE15-SP6-RT_Update_10 | 0 | 1-150600.1.5.1 |
| SUSE:Linux Enterprise Live Patching 15 SP6 | kernel-livepatch-SLE15-SP6_Update_10 | 0 | 1-150600.13.5.1 |
| SUSE:Linux Enterprise Live Patching 15 SP7 | kernel-default | 0 | 6.4.0-150700.53.3.1 |
| SUSE:Linux Enterprise Live Patching 15 SP7 | kernel-livepatch-SLE15-SP7_Update_1 | 0 | 1-150700.15.3.1 |
| SUSE:Linux Enterprise Module for Basesystem 15 SP6 | kernel-64kb | 0 | 6.4.0-150600.23.47.2 |
| SUSE:Linux Enterprise Module for Basesystem 15 SP6 | kernel-default | 0 | 6.4.0-150600.23.47.2 |
| SUSE:Linux Enterprise Module for Basesystem 15 SP6 | kernel-default-base | 0 | 6.4.0-150600.23.47.2.150600.12.20.2 |
| SUSE:Linux Enterprise Module for Basesystem 15 SP6 | kernel-source | 0 | 6.4.0-150600.23.47.2 |
| SUSE:Linux Enterprise Module for Basesystem 15 SP6 | kernel-zfcpdump | 0 | 6.4.0-150600.23.47.2 |
| SUSE:Linux Enterprise Module for Basesystem 15 SP7 | kernel-64kb | 0 | 6.4.0-150700.53.3.1 |
| SUSE:Linux Enterprise Module for Basesystem 15 SP7 | kernel-default | 0 | 6.4.0-150700.53.3.1 |
| SUSE:Linux Enterprise Module for Basesystem 15 SP7 | kernel-default-base | 0 | 6.4.0-150700.53.3.1.150700.17.2.1 |
| SUSE:Linux Enterprise Module for Basesystem 15 SP7 | kernel-source | 0 | 6.4.0-150700.53.3.1 |
| SUSE:Linux Enterprise Module for Basesystem 15 SP7 | kernel-zfcpdump | 0 | 6.4.0-150700.53.3.1 |
| SUSE:Linux Enterprise Module for Confidential Computing Technical Preview 15 SP6 | kernel-coco | 0 | 6.4.0-15061.21.coco15sp6.1 |
| SUSE:Linux Enterprise Module for Confidential Computing Technical Preview 15 SP6 | kernel-coco_debug | 0 | 6.4.0-15061.21.coco15sp6.1 |
| SUSE:Linux Enterprise Module for Confidential Computing Technical Preview 15 SP6 | kernel-source-coco | 0 | 6.4.0-15061.21.coco15sp6.1 |
| SUSE:Linux Enterprise Module for Confidential Computing Technical Preview 15 SP6 | kernel-syms-coco | 0 | 6.4.0-15061.21.coco15sp6.1 |
| SUSE:Linux Enterprise Module for Development Tools 15 SP6 | kernel-docs | 0 | 6.4.0-150600.23.47.1 |
| SUSE:Linux Enterprise Module for Development Tools 15 SP6 | kernel-obs-build | 0 | 6.4.0-150600.23.47.1 |
| SUSE:Linux Enterprise Module for Development Tools 15 SP6 | kernel-source | 0 | 6.4.0-150600.23.47.2 |
| SUSE:Linux Enterprise Module for Development Tools 15 SP6 | kernel-syms | 0 | 6.4.0-150600.23.47.1 |
| SUSE:Linux Enterprise Module for Development Tools 15 SP7 | kernel-docs | 0 | 6.4.0-150700.53.3.1 |
| SUSE:Linux Enterprise Module for Development Tools 15 SP7 | kernel-obs-build | 0 | 6.4.0-150700.53.3.1 |
| SUSE:Linux Enterprise Module for Development Tools 15 SP7 | kernel-source | 0 | 6.4.0-150700.53.3.1 |
| SUSE:Linux Enterprise Module for Development Tools 15 SP7 | kernel-syms | 0 | 6.4.0-150700.53.3.1 |
| SUSE:Linux Enterprise Module for Legacy 15 SP6 | kernel-default | 0 | 6.4.0-150600.23.47.2 |
| SUSE:Linux Enterprise Module for Legacy 15 SP7 | kernel-default | 0 | 6.4.0-150700.53.3.1 |
| SUSE:Linux Enterprise Module for Public Cloud 15 SP6 | kernel-azure | 0 | 6.4.0-150600.8.34.2 |
| SUSE:Linux Enterprise Module for Public Cloud 15 SP6 | kernel-source-azure | 0 | 6.4.0-150600.8.34.2 |
| SUSE:Linux Enterprise Module for Public Cloud 15 SP6 | kernel-syms-azure | 0 | 6.4.0-150600.8.34.1 |
| SUSE:Linux Enterprise Module for Public Cloud 15 SP7 | kernel-azure | 0 | 6.4.0-150700.20.3.1 |
| SUSE:Linux Enterprise Module for Public Cloud 15 SP7 | kernel-source-azure | 0 | 6.4.0-150700.20.3.1 |
| SUSE:Linux Enterprise Module for Public Cloud 15 SP7 | kernel-syms-azure | 0 | 6.4.0-150700.20.3.1 |
| SUSE:Linux Enterprise Workstation Extension 15 SP6 | kernel-default | 0 | 6.4.0-150600.23.47.2 |
| SUSE:Linux Enterprise Workstation Extension 15 SP7 | kernel-default | 0 | 6.4.0-150700.53.3.1 |
| SUSE:Real Time Module 15 SP6 | kernel-rt | 0 | 6.4.0-150600.10.34.1 |
| SUSE:Real Time Module 15 SP6 | kernel-rt_debug | 0 | 6.4.0-150600.10.34.1 |
| SUSE:Real Time Module 15 SP6 | kernel-source-rt | 0 | 6.4.0-150600.10.34.1 |
| SUSE:Real Time Module 15 SP6 | kernel-syms-rt | 0 | 6.4.0-150600.10.34.1 |
| Ubuntu:24.10 | linux-aws | 0 | 6.11.0-1014.15 |
| openSUSE:Leap 15.6 | dtb-aarch64 | 0 | 6.4.0-150600.23.47.1 |
| openSUSE:Leap 15.6 | kernel-64kb | 0 | 6.4.0-150600.23.47.2 |
| openSUSE:Leap 15.6 | kernel-azure | 0 | 6.4.0-150600.8.34.2 |
| openSUSE:Leap 15.6 | kernel-debug | 0 | 6.4.0-150600.23.47.2 |
| openSUSE:Leap 15.6 | kernel-default | 0 | 6.4.0-150600.23.47.2 |
| openSUSE:Leap 15.6 | kernel-default-base | 0 | 6.4.0-150600.23.47.2.150600.12.20.2 |
| openSUSE:Leap 15.6 | kernel-docs | 0 | 6.4.0-150600.23.47.1 |
| openSUSE:Leap 15.6 | kernel-kvmsmall | 0 | 6.4.0-150600.23.47.2 |
| openSUSE:Leap 15.6 | kernel-obs-build | 0 | 6.4.0-150600.23.47.1 |
| openSUSE:Leap 15.6 | kernel-obs-qa | 0 | 6.4.0-150600.23.47.1 |
| openSUSE:Leap 15.6 | kernel-rt | 0 | 6.4.0-150600.10.34.1 |
| openSUSE:Leap 15.6 | kernel-rt_debug | 0 | 6.4.0-150600.10.34.1 |
| openSUSE:Leap 15.6 | kernel-source | 0 | 6.4.0-150600.23.47.2 |
| openSUSE:Leap 15.6 | kernel-source-azure | 0 | 6.4.0-150600.8.34.2 |
| openSUSE:Leap 15.6 | kernel-source-rt | 0 | 6.4.0-150600.10.34.1 |
| openSUSE:Leap 15.6 | kernel-syms | 0 | 6.4.0-150600.23.47.1 |
| openSUSE:Leap 15.6 | kernel-syms-azure | 0 | 6.4.0-150600.8.34.1 |
| openSUSE:Leap 15.6 | kernel-syms-rt | 0 | 6.4.0-150600.10.34.1 |
| openSUSE:Leap 15.6 | kernel-zfcpdump | 0 | 6.4.0-150600.23.47.2 |
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