CVE-2026-43057
Published: 01 May 2026
Summary
CVE-2026-43057 is a high-severity an unspecified weakness vulnerability in Linux Linux Kernel. Its CVSS base score is 7.5 (High).
Operationally, exploitation aligns with the MITRE ATT&CK technique Application or System Exploitation (T1499.004); ranked at the 22.8th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog.
The strongest mitigations our analysis identified are NIST 800-53 SI-2 (Flaw Remediation) and SC-5 (Denial-of-service Protection).
Deeper analysis
CVE-2026-43057 is a vulnerability in the Linux kernel's networking stack, specifically affecting the handling of tunneled IPv6 traffic during GSO fallback for NETIF_F_IPV6_CSUM checksum offload. The feature advertises support only for packets without IPv6 extension headers, requiring software checksumming and GSO reversion for others, as TSO relies on offload. A prior commit implemented fallback by checking network header length, but it failed to account for tunneled packets, where the inner header length should be checked instead. This also mishandles special cases like tunneled packets without an inner IP protocol, such as RFC 6951 SCTP encapsulated in UDP, forcing incorrect paths.
Remote unauthenticated attackers can exploit this over the network with low complexity by sending crafted tunneled IPv6 packets that trigger the flawed fallback logic. Successful exploitation leads to a denial-of-service condition with high availability impact (CVSS 7.5: AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H), potentially causing kernel crashes or severe performance degradation in affected systems processing such traffic.
Mitigation requires applying upstream kernel patches from the referenced stable commits, including https://git.kernel.org/stable/c/2094a7cf91b71367b649f991aacc7b579f793d0b (extending checks for inner headers), https://git.kernel.org/stable/c/33670f780e0120c3dacda188c512bbffe0b6044c, https://git.kernel.org/stable/c/732fdeb2987c94b439d51f5cb9addddc2fc48c42, https://git.kernel.org/stable/c/a98b78116a27e2a57b696b569b2cb431c95cf9b6, and https://git.kernel.org/stable/c/c4336a07eb6b2526dc2b62928b5104b41a7f81f5, which correct the header length checks for tunneled scenarios.
EU & UK References
- 🇪🇺 ENISA EUVD: EUVD-2026-26656
Vulnerability details
In the Linux kernel, the following vulnerability has been resolved: net: correctly handle tunneled traffic on IPV6_CSUM GSO fallback NETIF_F_IPV6_CSUM only advertises support for checksum offload of packets without IPv6 extension headers. Packets with extension headers must fall back onto…
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software checksumming. Since TSO depends on checksum offload, those must revert to GSO. The below commit introduces that fallback. It always checks network header length. For tunneled packets, the inner header length must be checked instead. Extend the check accordingly. A special case is tunneled packets without inner IP protocol. Such as RFC 6951 SCTP in UDP. Those are not standard IPv6 followed by transport header either, so also must revert to the software GSO path.
- CWE(s)
Related Threats
MITRE ATT&CK Enterprise TechniquesAI
Why these techniques?
Vulnerability in Linux kernel networking stack allows remote unauthenticated attackers to send crafted tunneled IPv6 packets triggering flawed GSO fallback logic, directly enabling Endpoint Denial of Service through system exploitation leading to kernel crashes or performance degradation.
CVEs Like This One
Affected Assets
Mitigating Controls
Mitigating Controls (NIST 800-53 r5) AI
Flaw remediation directly mitigates CVE-2026-43057 by applying specific Linux kernel patches that correct the inner header length checks for tunneled IPv6 GSO fallback, preventing kernel crashes and performance degradation from crafted packets.
Denial-of-service protection implements network rate limiting and filtering to reduce the impact of crafted tunneled IPv6 packets exploiting the kernel's flawed fallback logic.
Boundary protection uses firewalls or intrusion prevention systems to monitor and block malformed tunneled IPv6 traffic at network boundaries before it triggers the vulnerable kernel processing path.