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How CVE-2026-52993 Works
The Linux kernel’s Transparent Inter-Process Communication (TIPC) protocol suffers from a double‑free vulnerability in the `tipc_buf_append()` function, located in net/tipc/msg.c. TIPC is a high‑performance, message‑oriented communication protocol used primarily in cluster environments for reliable intra‑node and inter‑node messaging.
The core of the issue lies in the interaction between `tipc_buf_append()` and tipc_msg_validate(). The `tipc_msg_validate()` function is responsible for verifying the integrity of a received TIPC message. Under certain conditions – for instance, when the message is fragmented and needs reassembly – `tipc_msg_validate()` can reallocate the socket buffer (skb) that it is validating. This reallocation frees the original skb and returns a new one.
In the vulnerable code, `tipc_buf_append()` called `tipc_msg_validate()` with a copy of the caller’s skb pointer (stored in a local variable). If the validation succeeded, no problem occurred. However, if validation failed after the reallocation, the error‑handling path would attempt to free the original skb pointer – which had already been freed by the reallocation – leading to a double‑free condition. This double‑free corrupts the kernel’s memory allocator state and can cause system instability, kernel panics, or, in more severe scenarios, arbitrary code execution.
The vulnerability was introduced in kernel version 4.15 with commit `d618d09a68e4` (“tipc: enforce valid ratio between skb truesize and contents”). The fix, applied in April 2026 and backported to all stable branches, eliminates the double‑free by passing the caller’s pointer‑to‑pointer directly to tipc_msg_validate(), so that any reallocation is correctly reflected. The local pointer is then updated from the (possibly modified) caller’s pointer before the error path is taken.
DailyCVE Form
Platform: Linux Kernel
Version: 4.15 – 6.18 (unpatched)
Vulnerability: Double‑free in tipc_buf_append()
Severity: High (CVSS 7.0)
Date: 2026‑06‑24
Prediction: Already patched in stable kernels
What Undercode Say: Analytics
Affected Versions
- Introduced in: `4.15` (commit
d618d09a68e4) - Fixed in:
– `5.10.258` (commita438975a6dcd)
– `5.15.209` (commit4ee4deadaae7)
– `6.1.175` (commitd3556656c6da)
– `6.6.141` (commit0274f24485fc)
– `6.12.91` (commit4d104882bc81)
– `6.18.33` (commit1d5e58905588)
– `7.0.10` (commit29940fff1411)
– `7.1` (commitd293ca716e7d)
Check Your Kernel Version
uname -r
Verify if the Fix Is Applied
Check if the commit is present in your kernel source (if building from git) git log --oneline | grep -E "a438975a6dcd|4ee4deadaae7|d3556656c6da|0274f24485fc|4d104882bc81|1d5e58905588|29940fff1411|d293ca716e7d"
Vulnerable Code Snippet (before fix)
int tipc_buf_append(struct sk_buff headbuf, struct sk_buff buf)
{
...
if (fragid == LAST_FRAGMENT) {
TIPC_SKB_CB(head)->validated = 0;
if (unlikely(!tipc_msg_validate(&head))) // head is a local copy
goto err; // double-free here
buf = head;
...
}
err:
kfree_skb(head); // frees the already-freed original skb
...
}
Patched Code (after fix)
int tipc_buf_append(struct sk_buff headbuf, struct sk_buff buf)
{
...
if (fragid == LAST_FRAGMENT) {
TIPC_SKB_CB(head)->validated = 0;
if (unlikely(!tipc_msg_validate(headbuf))) // pass pointer-to-pointer
goto err;
head = headbuf; // update from caller
buf = head;
...
}
err:
kfree_skb(head); // now frees the correct (possibly new) skb
...
}
Exploit
An attacker with local access to a system running an affected kernel can trigger the double‑free by sending a specially crafted sequence of TIPC messages that cause `tipc_msg_validate()` to reallocate the skb and then fail validation. The error path then frees an already‑freed memory region, corrupting the kernel’s memory allocator.
While the primary impact is a denial of service (kernel panic or system crash), memory corruption vulnerabilities of this nature can sometimes be leveraged for privilege escalation or arbitrary code execution – especially if the attacker can control the freed memory’s content and layout.
Exploit prerequisites:
- Local user with ability to create TIPC sockets (CAP_NET_ADMIN or unprivileged user on some distributions)
- TIPC module loaded (
modprobe tipc) - Knowledge of the target kernel version
Conceptual trigger (pseudo‑code):
// Create a TIPC socket sock = socket(AF_TIPC, SOCK_RDM, 0); // Send a fragmented message that will cause validation to reallocate and fail sendmsg(sock, ...); // crafted payload
No public exploit has been released as of the publication date, but the vulnerability is considered highly likely to be weaponized given the clarity of the bug and the availability of the fix.
Protection
- Immediate – Upgrade to a patched kernel version listed above.
- Workaround – If upgrading is not possible, disable the TIPC module:
modprobe -r tipc echo "blacklist tipc" >> /etc/modprobe.d/blacklist.conf
(Note: This will break any applications relying on TIPC.)
- Mitigation – Apply the kernel patch manually if you build your own kernel. The patch is minimal and has been backported to all stable trees.
- Monitoring – Look for kernel logs containing “tipc” or “double-free” warnings, and enable KASAN (Kernel Address Sanitizer) in development environments to catch such bugs early.
Impact
- Confidentiality – High (potential for arbitrary code execution leading to data leakage)
- Integrity – High (attacker may modify kernel memory)
- Availability – High (kernel panic or system crash)
- Attack Vector – Local (requires ability to create TIPC sockets)
- Complexity – Medium (requires crafted TIPC messages)
- Privileges – Low (unprivileged local user may trigger the bug on some configurations)
The vulnerability affects a wide range of Linux distributions that include the TIPC module, including Red Hat Enterprise Linux 8, 9, and 10, as well as many enterprise and embedded systems. Given the local attack vector, the most immediate risk is to multi‑user environments and cloud/container hosts where a malicious local user could crash the entire system.
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Sources:
Reported By: nvd.nist.gov
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