high CVSS 7.4 EPSS <0.1%

CVE-2024-27394·Kernel vulnerability

In the Linux kernel, the following vulnerability has been resolved: tcp: Fix Use-After-Free in tcp_ao_connect_init Since call_rcu, which is called in the hlist_for_each_entry_rcu traversal of tcp_ao_connect_init, is not part of the RCU read critical section, it is possible that the RCU grace period will pass during the traversal and the key will be free. To prevent this, it should be changed to hlist_for_each_entry_safe.

Severity
high
Software
Kernel
Fixed in
6.8.9
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 6% 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-2024-27394 scores 7.4 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: 6.7

Until: 6.8.9

Fixed in: 6.8.9

How to fix this CVE

Update your Linux kernel to version 6.8.9 or later to resolve a use-after-free vulnerability in TCP authentication option (TCP-AO) connection initialization. This flaw allows memory safety issues during RCU traversal when establishing authenticated TCP connections. Prioritize this update for systems handling sensitive network communications that rely on TCP-AO.

sudo dnf update kernel kernel-devel

Defensia detects this vulnerability

How to check if you are affected

  1. Step 1: Check your kernel version with `uname -r` and compare against the affected range 6.7 to 6.8.9
  2. Step 2: Verify TCP-AO is enabled in your kernel config by checking `grep CONFIG_TCP_AO /boot/config-$(uname -r)` for a value of 'y' or 'm'
  3. Step 3: Search system logs for TCP connection errors or kernel warnings related to RCU or TCP authentication using `sudo journalctl -xe | grep -i 'tcp\|rcu\|use.after.free'`
  4. Step 4: After patching, confirm the new kernel version with `uname -r` and verify it is 6.8.9 or later

FAQ

What is CVE-2024-27394?

This vulnerability is a use-after-free bug in the Linux kernel's TCP Authentication Option (TCP-AO) initialization routine. During connection setup, a memory management race condition can occur where RCU (Read-Copy-Update) allows memory to be freed while still being accessed, potentially leading to information disclosure or denial of service.

Is CVE-2024-27394 being actively exploited?

No, there is no evidence of active exploitation in the wild, and this vulnerability is not listed in CISA's Known Exploited Vulnerabilities (KEV) catalog. However, it should still be patched promptly as a high-severity kernel vulnerability.

What versions of Kernel are affected by CVE-2024-27394?

Linux kernel versions 6.7 through 6.8.8 are vulnerable. The vulnerability is patched in kernel 6.8.9 and later releases.

How do I check if my server is vulnerable to CVE-2024-27394?

Run `uname -r` to display your kernel version. If it reports a version between 6.7 and 6.8.8 inclusive, your system is vulnerable. Additionally, check if TCP-AO support is compiled into your kernel with `grep CONFIG_TCP_AO /boot/config-$(uname -r)`.

Does Defensia detect CVE-2024-27394?

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-2024-27394 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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