Linux Kernel up to 7.1.4 dst_metadata lib/string_helpers.c tun_dst_unclone buffer overflow

Summaryinfo

A vulnerability classified as very critical was found in Linux Kernel up to 7.1.4. Affected by this vulnerability is the function tun_dst_unclone of the file lib/string_helpers.c of the component dst_metadata. Executing a manipulation can lead to buffer overflow. This vulnerability is registered as CVE-2026-80615. It is possible to launch the attack remotely. No exploit is available.

Detailsinfo

A vulnerability classified as very critical was found in Linux Kernel up to 7.1.4. This vulnerability affects the function tun_dst_unclone of the file lib/string_helpers.c of the component dst_metadata. The manipulation with an unknown input leads to a buffer overflow vulnerability. The CWE definition for the vulnerability is CWE-120. The product copies an input buffer to an output buffer without verifying that the size of the input buffer is less than the size of the output buffer, leading to a buffer overflow. As an impact it is known to affect confidentiality, integrity, and availability. CVE summarizes:

In the Linux kernel, the following vulnerability has been resolved: net: dst_metadata: fix false-positive memcpy overflow in tun_dst_unclone kmalloc_flex() in metadata_dst_alloc() sets __counted_by for the structure to the options_len, which is then initialized to zero. Later, we're initializing the structure by copying the tunnel info together with the options, and this triggers a warning for a potential memcpy overflow, since the compiler estimates that the options can't fit into the structure, even though the memory for them is actually allocated. memcpy: detected buffer overflow: 104 byte write of buffer size 96 WARNING: CPU: X PID: Y at lib/string_helpers.c:1036 __fortify_report skb_tunnel_info_unclone+0x179/0x190 geneve_xmit+0x7fe/0xe00 The issue is triggered when built with clang and source fortification. Fix that by doing the copy in two stages: first - the main data with the options_len, then the options. This way the correct length should be known at the time of the copy. It would be better if the options_len never changed after allocation, but the allocation code is a little separate from the initialization and it would be awkward and potentially dangerous to return a struct with options_len set to a non-zero value from the metadata_dst_alloc(). Another option would be to use ip_tunnel_info_opts_set(), but it is doing too many unnecessary operations for the use case here.

The advisory is available at git.kernel.org. This vulnerability was named CVE-2026-80615 since 08/26/2026. The exploitation appears to be easy. The attack can be initiated remotely. No form of authentication is required for a successful exploitation. Technical details are known, but there is no available exploit. The structure of the vulnerability defines a possible price range of USD $5k-$25k at the moment (estimation calculated on 08/28/2026).

Upgrading to version 7.1.5 eliminates this vulnerability. Applying the patch 7ce31739fe88a558370135db95bbeec1e7ddfc29/4c6d43db2a4d2cef3921e885cf34798f790d34ea is able to eliminate this problem.

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Productinfo

Type

• Operating System

Vendor

• Linux

Name

• Kernel

Version

• 7.1.0
• 7.1.1
• 7.1.2
• 7.1.3
• 7.1.4

License

• open-source

Website

• Vendor: https://www.kernel.org/

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