Linux Kernel nexthop weight/resvd1 allocation of resources

Summaryinfo

A vulnerability was found in Linux Kernel. It has been classified as very critical. This affects an unknown function of the component nexthop. Performing a manipulation of the argument weight/resvd1 results in allocation of resources. This vulnerability is known as CVE-2024-14040. Remote exploitation of the attack is possible. No exploit is available.

Detailsinfo

A vulnerability was found in Linux Kernel (unknown version). It has been classified as very critical. This affects an unknown code block of the component nexthop. The manipulation of the argument weight/resvd1 with an unknown input leads to a allocation of resources vulnerability. CWE is classifying the issue as CWE-770. The product allocates a reusable resource or group of resources on behalf of an actor without imposing any restrictions on the size or number of resources that can be allocated, in violation of the intended security policy for that actor. This is going to have an impact on confidentiality, integrity, and availability. The summary by CVE is:

In the Linux kernel, the following vulnerability has been resolved: net: nexthop: Increase weight to u16 In CLOS networks, as link failures occur at various points in the network, ECMP weights of the involved nodes are adjusted to compensate. With high fan-out of the involved nodes, and overall high number of nodes, a (non-)ECMP weight ratio that we would like to configure does not fit into 8 bits. Instead of, say, 255:254, we might like to configure something like 1000:999. For these deployments, the 8-bit weight may not be enough. To that end, in this patch increase the next hop weight from u8 to u16. Increasing the width of an integral type can be tricky, because while the code still compiles, the types may not check out anymore, and numerical errors come up. To prevent this, the conversion was done in two steps. First the type was changed from u8 to a single-member structure, which invalidated all uses of the field. This allowed going through them one by one and audit for type correctness. Then the structure was replaced with a vanilla u16 again. This should ensure that no place was missed. The UAPI for configuring nexthop group members is that an attribute NHA_GROUP carries an array of struct nexthop_grp entries: struct nexthop_grp { __u32 id; /* nexthop id - must exist */ __u8 weight; /* weight of this nexthop */ __u8 resvd1; __u16 resvd2; }; The field resvd1 is currently validated and required to be zero. We can lift this requirement and carry high-order bits of the weight in the reserved field: struct nexthop_grp { __u32 id; /* nexthop id - must exist */ __u8 weight; /* weight of this nexthop */ __u8 weight_high; __u16 resvd2; }; Keeping the fields split this way was chosen in case an existing userspace makes assumptions about the width of the weight field, and to sidestep any endianness issues. The weight field is currently encoded as the weight value minus one, because weight of 0 is invalid. This same trick is impossible for the new weight_high field, because zero must mean actual zero. With this in place: - Old userspace is guaranteed to carry weight_high of 0, therefore configuring 8-bit weights as appropriate. When dumping nexthops with 16-bit weight, it would only show the lower 8 bits. But configuring such nexthops implies existence of userspace aware of the extension in the first place. - New userspace talking to an old kernel will work as long as it only attempts to configure 8-bit weights, where the high-order bits are zero. Old kernel will bounce attempts at configuring >8-bit weights. Renaming reserved fields as they are allocated for some purpose is commonly done in Linux. Whoever touches a reserved field is doing so at their own risk. nexthop_grp::resvd1 in particular is currently used by at least strace, however they carry an own copy of UAPI headers, and the conversion should be trivial. A helper is provided for decoding the weight out of the two fields. Forcing a conversion seems preferable to bending backwards and introducing anonymous unions or whatever.

The advisory is shared at git.kernel.org. This vulnerability is uniquely identified as CVE-2024-14040 since 07/26/2026. The exploitability is told to be easy. It is possible to initiate the attack remotely. The exploitation requires an enhanced level of successful authentication. Technical details are known, but no exploit is available. The price for an exploit might be around USD $0-$5k at the moment (estimation calculated on 07/29/2026). MITRE ATT&CK project uses the attack technique T1499 for this issue.

The vulnerability scanner Nessus provides a plugin with the ID 330018 (Linux Distros Unpatched Vulnerability : CVE-2024-14040), which helps to determine the existence of the flaw in a target environment.

Applying the patch b72a6a7ab9573e06d5c2fcb92eaa28614a735bfd is able to eliminate this problem.

The vulnerability is also documented in the databases at Tenable (330018), EUVD (EUVD-2024-55701) and CERT Bund (WID-SEC-2026-2527). If you want to get the best quality for vulnerability data then you always have to consider VulDB.

Affected

• Red Hat Enterprise Linux
• Ubuntu Linux
• Open Source Linux Kernel

Productinfo

Type

• Operating System

Vendor

• Linux

Name

• Kernel

License

• open-source

Website

• Vendor: https://www.kernel.org/

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Entryinfo

If you want to get the best quality for vulnerability data then you always have to consider VulDB.

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