medium CVSS 6.3 EPSS <0.1%

CVE-2023-52581·Kernel vulnerability

In the Linux kernel, the following vulnerability has been resolved: netfilter: nf_tables: fix memleak when more than 255 elements expired When more than 255 elements expired we're supposed to switch to a new gc container structure. This never happens: u8 type will wrap before reaching the boundary and nft_trans_gc_space() always returns true. This means we recycle the initial gc container structure and lose track of the elements that came before. While at it, don't deref 'gc' after we've passed it to call_rcu.

Severity
medium
Software
Kernel
Fixed in
6.5.6
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% — in the bottom 1% 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.

Affected versions

From: 6.5

Until: 6.5.6

Fixed in: 6.5.6

How to fix this CVE

Update your Linux kernel to version 6.5.6 or later to resolve a memory leak in the netfilter nf_tables garbage collection subsystem. This vulnerability affects systems running kernel versions 6.5 through 6.5.5, where improper element expiration handling causes memory to be lost when processing large batches of firewall rules. Apply the kernel update through your distribution's package manager and reboot to activate the patched kernel.

sudo dnf upgrade kernel kernel-core kernel-modules

Defensia detects this vulnerability

How to check if you are affected

  1. Check installed kernel version: uname -r — verify it is 6.5.6 or later
  2. Confirm netfilter nf_tables module is loaded: lsmod | grep nf_tables — if empty, component is not exposed
  3. Review syslog for memory allocation failures: grep -i 'memory\|alloc\|gc' /var/log/syslog | tail -100 — look for patterns during peak firewall rule activity
  4. Verify patch installation: grep -i CONFIG_NF_TABLES /boot/config-$(uname -r) — should show CONFIG_NF_TABLES=y or =m, and kernel version should be 6.5.6+

FAQ

What is CVE-2023-52581?

This vulnerability is a memory leak in the Linux kernel's netfilter nf_tables subsystem where the garbage collection mechanism fails to properly track expired firewall rule elements when more than 255 expire simultaneously, causing allocated memory to be orphaned and unreclaimable.

Is CVE-2023-52581 being actively exploited?

No, there is no evidence of active exploitation in the wild. This is a reliability/denial-of-service risk rather than a remote code execution vector.

What versions of Kernel are affected by CVE-2023-52581?

Linux kernel versions 6.5 through 6.5.5 are affected. Version 6.5.6 and later contain the fix.

How do I check if my server is vulnerable to CVE-2023-52581?

Run 'uname -r' to get your kernel version. If it shows 6.5.0 through 6.5.5, your system is vulnerable. Additionally, check if nf_tables is in use with 'lsmod | grep nf_tables'.

Does Defensia detect CVE-2023-52581?

Yes — Defensia's CVE advisory scanner compares installed package versions against the NVD database. If Kernel is installed on a monitored server, CVE-2023-52581 will appear in your dashboard with remediation steps.

Related Kernel CVEs

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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.
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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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