A recent security vulnerability has been identified and remedied in the Linux kernel, specifically in the netfilter module. The Common Vulnerabilities and Exposures (CVE) system has assigned the identifier CVE-2023-52620 to this issue. This post will provide an in-depth look at the vulnerability, including the issue it presents, the resolution, and code snippets demonstrating these changes.

Vulnerability Details

At the heart of CVE-2023-52620 lies the netfilter subsystem of the Linux kernel, which is responsible for implementing packet filtering, the translation of network addresses (NAT), and other packet manipulation. The specific component of netfilter affected by this vulnerability is the "nf_tables" module. The issue arises from the ability to set a timeout for anonymous (unnamed) sets, which is not used from userspace and as such, should not be allowed. Allowing timeouts for anonymous sets presents a security risk and can potentially lead to a compromised system.

Resolution

To fix this vulnerability, the support for setting timeouts for anonymous sets in the nf_tables module has been removed. This ensures that attackers cannot exploit the feature to compromise system security. The following code snippet demonstrates the change that has been made to address CVE-2023-52620:

/* old vulnerable code */
static int nft_setelem_parse(struct nft_ctx *ctx, const struct nft_set *set,
            struct nft_userdata *udata)
{
  ...
  if (set->flags & NFT_SET_ANONYMOUS)
    timeout = U32_MAX;
  ...
}

/* new patched code */
static int nft_setelem_parse(struct nft_ctx *ctx, const struct nft_set *set,
            struct nft_userdata *udata)
{
  ...
  if (set->flags & NFT_SET_ANONYMOUS) {
    if (timeout != U32_MAX)
      return -EINVAL;
  }
  ...
}

By checking if the timeout is not equal to U32_MAX in the case of anonymous sets and returning an error if it is not, we can effectively disallow timeouts for anonymous sets and mitigate the vulnerability.

Original References

The complete set of changes made to address this vulnerability can be found in the official Linux kernel repository in the form of a patch. Additionally, the mailing list post announcing the patch is available for further information:
- Linux kernel patch
- Mailing list post

Conclusion

In summary, the Linux kernel has addressed a security vulnerability, CVE-2023-52620, in the netfilter subsystem. By disallowing timeouts for anonymous set objects in the nf_tables module, the potential for system compromise has been mitigated. This post provided a comprehensive analysis of the issue, the resolution, and the corresponding code changes. It is essential to keep your Linux kernel up-to-date in order to ensure your system is as secure as possible against known vulnerabilities.

Timeline

Published on: 03/21/2024 11:15:28 UTC
Last modified on: 11/06/2024 20:35:08 UTC