high CVSS 8.1 EPSS <0.1%

CVE-2025-21760·Kernel vulnerability

In the Linux kernel, the following vulnerability has been resolved: ndisc: extend RCU protection in ndisc_send_skb() ndisc_send_skb() can be called without RTNL or RCU held. Acquire rcu_read_lock() earlier, so that we can use dev_net_rcu() and avoid a potential UAF.

Severity
high
Software
Kernel
Fixed in
6.13.4
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 14% 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-2025-21760 scores 8.1 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: 6.13.4

Fixed in: 6.13.4

How to fix this CVE

Update your Linux kernel to version 6.13.4 or later to resolve a use-after-free vulnerability in the NDISC (Neighbor Discovery) subsystem. This vulnerability could allow a local attacker with limited privileges to cause a kernel crash or potentially execute arbitrary code. Apply the kernel update through your distribution's package manager and reboot your system to complete the remediation.

sudo dnf update kernel kernel-devel && sudo reboot

Defensia detects this vulnerability

How to check if you are affected

  1. Check your current kernel version by running: uname -r
  2. Verify if you are running a vulnerable version (6.13.0 through 6.13.3) by comparing against the output above
  3. Inspect kernel logs for NDISC-related crashes: sudo dmesg | grep -i 'ndisc\|use.after.free\|uaf'
  4. After patching, confirm the kernel version has been updated to 6.13.4 or later and verify the system has rebooted: uname -r

FAQ

What is CVE-2025-21760?

CVE-2025-21760 is a use-after-free vulnerability in the Linux kernel's NDISC (Neighbor Discovery) protocol handler. The flaw occurs when the ndisc_send_skb() function is called without proper RCU (Read-Copy-Update) synchronization, allowing a local attacker to trigger a memory access violation.

Is CVE-2025-21760 being actively exploited?

No, CVE-2025-21760 is not listed in CISA's Known Exploited Vulnerabilities (KEV) catalog and there are no publicly available exploits at this time. However, the vulnerability's local attack vector and high severity score warrant prompt patching.

What versions of Kernel are affected by CVE-2025-21760?

Linux kernel versions 6.13.0 through 6.13.3 are affected. The vulnerability was fixed in kernel version 6.13.4 and later.

How do I check if my server is vulnerable to CVE-2025-21760?

Run 'uname -r' and check if your kernel version falls within the 6.13.0 to 6.13.3 range. If it does, your system requires immediate patching.

Does Defensia detect CVE-2025-21760?

Yes — Defensia's CVE advisory scanner compares installed package versions against the NVD database. If the Linux kernel is installed on a monitored server, CVE-2025-21760 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.
CVE-2026-53221CVSS 9.8In the Linux kernel, the following vulnerability has been resolved: ip6_vti: fix incorrect tunnel matching in vti6_tnl_lookup() In vti6_tnl_lookup(), when an exact match for a tunnel fails, the code falls back to searching for wildcard tunnels: - Tunnels matching the packet's local address, with any remote address wildcard remote). - Tunnels matching the packet's remote address, with any local address (wildcard local). However, vti6 stores all these different types of tunnels in the same hash table (ip6n->tnls_r_l) prone to hash collisions. The bug is that the fallback search loops in vti6_tnl_lookup() were missing checks to ensure that the candidate tunnel actually has a wildcard address.
CVE-2026-53151CVSS 9.8In the Linux kernel, the following vulnerability has been resolved: rxrpc: Fix the ACK parser to extract the SACK table for parsing Fix modification of the received skbuff in rxrpc_input_soft_acks() and a potential incorrect access of the buffer in a fragmented UDP packet (the packet would probably have to be deliberately pre-generated as fragmented) when AF_RXRPC tries to extract the contents of the SACK table by copying out the contents of the SACK table into a buffer before attempting to parse AF_RXRPC assumes that it can just call skb_condense() and then validly access the SACK table from skb->data and that it will be a flat buffer - but skb_condense() can silently fail to do anything under some circumstances. Note that whilst rxrpc_input_soft_acks() should be able to parse extended ACKs, the rest of AF_RXRPC doesn't currently support that. Further, there's then no need to call skb_condense() in rxrpc_input_ack(), so don't.
CVE-2026-53088CVSS 9.8In the Linux kernel, the following vulnerability has been resolved: net: bcmgenet: fix off-by-one in bcmgenet_put_txcb The write_ptr points to the next open tx_cb. We want to return the tx_cb that gets rewinded, so we must rewind the pointer first then return the tx_cb that it points to. That way the txcb can be correctly cleaned up.
CVE-2026-53228CVSS 9.8In the Linux kernel, the following vulnerability has been resolved: ipv6: sit: reload inner IPv6 header after GSO offloads ipip6_tunnel_xmit() caches the inner IPv6 header pointer at function entry and continues using it after iptunnel_handle_offloads(). For GSO skbs, iptunnel_handle_offloads() calls skb_header_unclone(). When the skb header is cloned, skb_header_unclone() can call pskb_expand_head(), which may move the skb head. The pskb_expand_head() contract requires pointers into the skb header to be reloaded after the call. If the later skb_realloc_headroom() branch is not taken, SIT uses the stale iph6 pointer to read the inner hop limit and DS field. That can read from a freed skb head after the old head's remaining clone is released. Reload iph6 after the offload helper succeeds and before subsequent reads from the inner IPv6 header. Keep the existing reload after skb_realloc_headroom(), since that branch can also replace the skb.

References

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