CVE-2024-26642: Patching the Linux Kernel Netfilter Vulnerability - Unauthorized Anonymous Set with Timeout Flag

In recent days, a newly discovered vulnerability, assigned the CVE identifier CVE-2024-26642, has been causing headaches for Linux users everywhere. As with any vulnerabilities, it poses a potential threat to users and needs to be resolved swiftly and effectively. In this post, we dive deep into this vulnerability, discussing its implications, walking through the code snippet that resolves it, and shedding light on the measures taken to ensure this does not happen again.

Understanding the Vulnerability

Before going into the solution, let's take a moment to understand the vulnerability itself and its impact on the Linux kernel. The vulnerability in question is within the netfilter subsystem of the Linux kernel, specifically in the nf_tables module. This module is in charge of dealing with filtering and manipulation of network packets.

The vulnerability arises when anonymous sets are used with a timeout from userspace, which is an undesired and incorrect behavior that could lead to potential attacks or unexpected behavior. However, there is an exception to this rule, where the use of anonymous sets with a timeout is allowed for NFT_SET_EVAL, to ensure that legacy meters continue to work properly.

The Code Snippet

In order to fix this vulnerability, a simple patch had to be applied to the nf_tables module, to reject the use of anonymous sets with a timeout flag, as shown in the code snippet below:

/* ... */

static int nf_tables_newset(struct net *net, struct nft_ctx *ctx,
                const struct nlattr * const nla[])
{
    /* ... */

+    if (nla[NFTA_SET_DESC] && (flags & (NFT_SET_TIMEOUT | NFT_SET_ANONYMOUS)))
+        return -EINVAL;

+    if (desc.size && desc.size != NFT_SET_DESC_CONCAT_SIZE(desc))
+        return -EINVAL;

    /* ... */
}

/* ... */

The above lines of code were added to ensure that if there is a descriptor (NFTA_SET_DESC) and either the timeout flag (NFT_SET_TIMEOUT) or the anonymous flag (NFT_SET_ANONYMOUS) is present, then an invalid input error (-EINVAL) is returned. This effectively rejects the illegal combination of anonymous sets with a timeout flag.

Original References

For those interested in understanding the details of this patch and related discussions, the following resources provide a wealth of information:

1. Linux kernel commit that resolves the vulnerability: netfilter: nf_tables: disallow anonymous set with timeout flag

2. Security announcement by the Linux kernel developers: Linux kernel update announcement

3. CVE entry for the vulnerability: CVE-2024-26642 - National Vulnerability Database

Exploit Details

Although there are no publicly disclosed exploits for this vulnerability at the time of writing, the potential to abuse this vulnerability still exists. Attackers could misuse the anonymous set in network filtering or manipulations without being noticed by the user. By applying the patch, we ensure that incorrect usage patterns that potentially lead to unexpected behavior are curbed, thereby reducing the risk for Linux users.

Conclusion

The discovery and swift resolution of CVE-2024-26642 demonstrate the importance of continuous vigilance in the open-source community. Thanks to the dedicated work of the Linux kernel developers and the close collaboration of security-conscious users, an important vulnerability was quickly addressed. As Linux users, we can now breathe a sigh of relief and continue to rely on the secure and robust performance that has come to define the operating system.

Timeline

Published on: 03/21/2024 11:15:28 UTC
Last modified on: 12/19/2024 08:44:09 UTC