CVE-2024-36903 in Linux
Summary
by MITRE • 05/30/2024
In the Linux kernel, the following vulnerability has been resolved:
ipv6: Fix potential uninit-value access in __ip6_make_skb()
As it was done in commit fc1092f51567 ("ipv4: Fix uninit-value access in __ip_make_skb()") for IPv4, check FLOWI_FLAG_KNOWN_NH on fl6->flowi6_flags instead of testing HDRINCL on the socket to avoid a race condition which causes uninit-value access.
If you want to get best quality of vulnerability data, you may have to visit VulDB.
Analysis
by VulDB Data Team • 12/04/2025
The vulnerability CVE-2024-36903 addresses a critical uninitialized value access issue within the Linux kernel's IPv6 networking stack, specifically in the __ip6_make_skb() function. This flaw represents a classic security concern where uninitialized memory values could be inadvertently accessed during packet processing, potentially leading to information disclosure or system instability. The vulnerability manifests in the IPv6 implementation's handling of socket flags and flow information, creating a scenario where the kernel might operate on uninitialized data structures that should contain valid routing information.
The technical root cause stems from an inconsistent approach in how IPv6 flow information is validated compared to its IPv4 counterpart. The kernel's IPv6 implementation was incorrectly relying on the HDRINCL socket flag to determine whether network headers were already included in the packet, rather than properly checking the FLOWI_FLAG_KNOWN_NH flag within the flowi6_flags structure. This approach creates a race condition scenario where the kernel might access uninitialized memory fields during packet construction, particularly when dealing with certain types of IPv6 routing decisions and packet forwarding operations.
This vulnerability directly relates to CWE-457: Use of uninitialized variable, which is a fundamental security weakness that can lead to unpredictable behavior and potential exploitation. The flaw is particularly concerning because it occurs in kernel space where such issues can be leveraged to escalate privileges or cause denial of service conditions. The race condition aspect of this vulnerability means that timing-sensitive operations could trigger the uninitialized memory access, making it potentially exploitable in certain network traffic scenarios.
The operational impact of CVE-2024-36903 extends beyond simple kernel instability to potentially enable more sophisticated attacks. When uninitialized memory values are accessed during packet processing, attackers could theoretically extract sensitive information from kernel memory regions or cause the system to crash through invalid memory operations. The vulnerability affects systems running Linux kernel versions that include the affected code path, particularly those handling significant IPv6 network traffic or serving as routers and gateways. Network administrators should be aware that this issue could be exploited in environments where IPv6 traffic is processed, potentially allowing attackers to gain insights into kernel memory layout or cause system crashes.
The fix implemented for this vulnerability follows established security patterns by aligning the IPv6 implementation with the previously resolved IPv4 issue in commit fc1092f51567. This approach ensures consistency across the kernel's networking stack and prevents the race condition that led to uninitialized value access. The solution involves changing the validation logic from checking socket-specific HDRINCL flags to properly examining the FLOWI_FLAG_KNOWN_NH flag within the flow information structure, which provides a more reliable and consistent method for determining packet routing state. This remediation aligns with ATT&CK technique T1068: Exploitation for Privilege Escalation by preventing potential exploitation paths through uninitialized memory access vulnerabilities.
System administrators should prioritize patching affected systems with the kernel version containing the fix, particularly in environments handling substantial IPv6 traffic or serving critical network infrastructure roles. The vulnerability demonstrates the importance of maintaining consistent security practices across kernel subsystems and highlights the need for thorough testing of networking code paths that involve complex flow information handling and memory management. Organizations should also monitor for similar patterns in other kernel networking components that might exhibit analogous race condition vulnerabilities. The fix represents a defensive programming improvement that reduces the attack surface for kernel-based exploits while maintaining the expected functionality of IPv6 packet processing operations.