high CVSS 7.1 EPSS <0.1%

CVE-2025-21719·Kernel vulnerability

In the Linux kernel, the following vulnerability has been resolved: ipmr: do not call mr_mfc_uses_dev() for unres entries syzbot found that calling mr_mfc_uses_dev() for unres entries would crash [1], because c->mfc_un.res.minvif / c->mfc_un.res.maxvif alias to "struct sk_buff_head unresolved", which contain two pointers. This code never worked, lets remove it. [1] Unable to handle kernel paging request at virtual address ffff5fff2d536613 KASAN: maybe wild-memory-access in range [0xfffefff96a9b3098-0xfffefff96a9b309f] Modules linked in: CPU: 1 UID: 0 PID: 7321 Comm: syz.0.16 Not tainted 6.13.0-rc7-syzkaller-g1950a0af2d55 #0 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 09/13/2024 pstate: 80400005 (Nzcv daif +PAN -UAO -TCO -DIT -SSBS BTYPE=--) pc : mr_mfc_uses_dev net/ipv4/ipmr_base.c:290 [inline] pc : mr_table_dump+0x5a4/0x8b0 net/ipv4/ipmr_base.c:334 lr : mr_mfc_uses_dev net/ipv4/ipmr_base.c:289 [inline] lr : mr_table_dump+0x694/0x8b0 net/ipv4/ipmr_base.c:334 Call trace: mr_mfc_uses_dev net/ipv4/ipmr_base.c:290 [inline] (P) mr_table_dump+0x5a4/0x8b0 net/ipv4/ipmr_base.c:334 (P) mr_rtm_dumproute+0x254/0x454 net/ipv4/ipmr_base.c:382 ipmr_rtm_dumproute+0x248/0x4b4 net/ipv4/ipmr.c:2648 rtnl_dump_all+0x2e4/0x4e8 net/core/rtnetlink.c:4327 rtnl_dumpit+0x98/0x1d0 net/core/rtnetlink.c:6791 netlink_dump+0x4f0/0xbc0 net/netlink/af_netlink.c:2317 netlink_recvmsg+0x56c/0xe64 net/netlink/af_netlink.c:1973 sock_recvmsg_nosec net/socket.c:1033 [inline] sock_recvmsg net/socket.c:1055 [inline] sock_read_iter+0x2d8/0x40c net/socket.c:1125 new_sync_read fs/read_write.c:484 [inline] vfs_read+0x740/0x970 fs/read_write.c:565 ksys_read+0x15c/0x26c fs/read_write.c:708

Severity
high
Software
Kernel
Fixed in
6.13.2
Published

How likely is exploitation

FIRST's Exploit Prediction Scoring System puts the probability of this CVE being exploited in the next 30 days at <0.1% — higher than 11% of all published CVEs. EPSS is an independent forecast of exploitation, not a severity rating: it says nothing about how much damage a successful attack does, which is what a CVSS score measures.

Read the two together. CVE-2025-21719 scores 7.1 on CVSS, so a successful attack would be serious — but at <0.1%, almost nobody is currently attempting it. That is a different situation from a flaw under mass exploitation, and it is usually the difference between patching on your next maintenance window and patching tonight.

Affected versions

From: 6.13

Until: 6.13.2

Fixed in: 6.13.2

How to fix this CVE

Update the Linux kernel to version 6.13.2 or later to resolve a memory access violation in the multicast routing subsystem. This vulnerability affects kernel versions 6.13 through 6.13.1 and can cause a kernel panic when processing multicast forwarding cache entries. Apply the kernel update and reboot your system to fully remediate the issue.

sudo dnf update kernel kernel-devel && sudo reboot

Defensia detects this vulnerability

How to check if you are affected

  1. Check installed kernel version: uname -r — ensure it is 6.13.2 or later
  2. Verify multicast routing is enabled: cat /proc/net/ip_mr_cache — if empty, component is not active
  3. Search kernel logs for crashes: sudo journalctl -b | grep -i 'mr_mfc_uses_dev\|kernel paging request\|ipmr'
  4. Confirm fix was applied: dmesg | grep -i 'kernel.*6.13.2' or compare kernel version again with uname -r

FAQ

What is CVE-2025-21719?

CVE-2025-21719 is a memory corruption vulnerability in the Linux kernel's multicast routing (ipmr) module where uninitialized multicast forwarding cache entries are incorrectly dereferenced, causing a kernel crash due to wild memory access.

Is CVE-2025-21719 being actively exploited?

No, CVE-2025-21719 is not listed in the CISA Known Exploited Vulnerabilities catalog and no public exploits are currently available. However, it can be triggered by local attackers with low privileges.

What versions of Kernel are affected by CVE-2025-21719?

Linux kernel versions 6.13 through 6.13.1 are affected. The vulnerability was introduced in 6.13 and fixed in 6.13.2.

How do I check if my server is vulnerable to CVE-2025-21719?

Run 'uname -r' and compare your kernel version. If it shows 6.13.0 through 6.13.1, your system is vulnerable. Update to 6.13.2 or later immediately.

Does Defensia detect CVE-2025-21719?

Yes — Defensia's CVE advisory scanner compares installed package versions against the NVD database. If Kernel is installed on a monitored server, CVE-2025-21719 will appear in your dashboard with remediation steps.

Related Kernel CVEs

CVE-2026-63795CVSS 10In the Linux kernel, the following vulnerability has been resolved: 9p: avoid putting oldfid in p9_client_walk() error path When p9_client_walk() is called with clone set to false, fid aliases oldfid. If the walk subsequently fails after the request has been sent, the error path jumps to clunk_fid, which currently calls p9_fid_put(fid) unconditionally. This drops a reference to oldfid even though ownership of oldfid remains with the caller. If this is the last reference, oldfid can be clunked and destroyed while the caller still expects it to be valid. A later use or put of oldfid can then trigger a use-after-free or refcount underflow. Fix this by only putting fid in the clunk_fid error path when it does not alias oldfid, matching the existing guard in the error path below. This can be triggered when a multi-component walk is split into multiple p9_client_walk() calls and a later non-cloning walk fails. A reproducer and refcount warning logs are available on request.
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References

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