CVE-2026-74724 in Linux
Summary
by MITRE • 08/22/2026
In the Linux kernel, the following vulnerability has been resolved:
ipvs: avoid out-of-bounds write in ip_vs_nat_icmp
Sashiko warns that local attacker can modify the packet while it is processed by IPVS. Some places read the IP ihl field multiple times which can cause out-of-bounds access. One such place is ip_vs_nat_icmp where we can write after the validated area.
Fix it by providing ciph argument just like it is done for IPv6 and use ciph->len as offset to the embedded transport header.
Modify some IPv4 header checks by reading the ihl field only once.
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Analysis
by VulDB Data Team • 08/22/2026
The Linux kernel's IP Virtual Server (IPVS) subsystem, which provides load balancing capabilities across a cluster of servers, contains a critical memory safety vulnerability in its ICMP packet handling logic. Specifically, within the ip_vs_nat_icmp function, there exists an out-of-bounds write condition that arises from improper validation and access patterns regarding network header fields. This flaw is particularly concerning because it allows for potential exploitation by local attackers who can manipulate packets during processing, leading to memory corruption issues that could compromise system stability or security posture.
The root cause of this vulnerability lies in the inconsistent reading of the Internet Header Length (IHL) field within IPv4 headers. In several code paths, including ip_vs_nat_icmp, the IHL value is read multiple times without ensuring its consistency throughout the processing lifecycle. An attacker with local access can modify packet data while it resides in kernel memory buffers between these reads. If the IHL value changes or if the initial validation does not strictly bound subsequent accesses based on a single verified instance of this field, the kernel may calculate incorrect offsets for header traversal and modification. This discrepancy enables writes to occur beyond the validated boundaries of the packet buffer, resulting in an out-of-bounds write operation that can overwrite adjacent memory structures.
From a technical perspective, this vulnerability is classified under CWE-787: Out-of-Bounds Write, as it involves writing data past the end or before the beginning of the intended buffer. The operational impact includes potential kernel panics due to corrupted memory states, which leads to denial of service conditions for services relying on IPVS load balancing. Furthermore, in more severe scenarios where specific memory layouts are exploited, such out-of-bounds writes could potentially facilitate arbitrary code execution by overwriting critical control data structures within the kernel space. This aligns with ATT&CK technique T1059: Command and Scripting Interpreter if the exploitation leads to further lateral movement or privilege escalation via compromised system components.
To mitigate this vulnerability, the Linux kernel maintainers have implemented a fix that enforces strict consistency in header field validation. The solution involves introducing a ciph argument similar to the approach used for IPv6 processing, which ensures that the length of the encapsulated transport header is calculated using a single, validated instance of relevant fields rather than re-reading potentially mutable data multiple times. By utilizing ciph->len as the definitive offset to the embedded transport header, the code prevents discrepancies caused by concurrent packet modification. Additionally, IPv4 header checks have been refactored to read the IHL field only once per processing context, thereby eliminating the race condition window where an attacker could alter the value between reads. System administrators should apply kernel updates that include this patch immediately to restore memory safety guarantees within the IPVS subsystem and prevent potential exploitation of this out-of-bounds write flaw.