CVE-2026-68127 in Linux
Summary
by MITRE • 08/10/2026
In the Linux kernel, the following vulnerability has been resolved:
ila: reload IPv6 header after pskb_may_pull in checksum adjust
ila_csum_adjust_transport() caches ip6h = ipv6_hdr(skb) before calling pskb_may_pull(). On a non-linear skb whose transport header sits in a page fragment, pskb_may_pull() can call __pskb_pull_tail() / pskb_expand_head() and free the old skb head, leaving ip6h dangling; the following get_csum_diff(ip6h, p) then reads freed memory. ila_update_ipv6_locator() uses ip6h (and the iaddr derived from it) again after the csum-adjust call and additionally writes the new locator through that pointer.
Impact: a remote IPv6 packet routed through a configured ILA csum-adjust-transport route or receive-side mapping triggers a slab-use-after-free in ila_update_ipv6_locator() (KASAN). The route or mapping requires CAP_NET_ADMIN to configure, but trigger packets are unauthenticated once it exists.
Reload ip6h after each pskb_may_pull() in ila_csum_adjust_transport() before the csum-diff read. In ila_update_ipv6_locator() only the ILA_CSUM_ADJUST_TRANSPORT case pulls the skb, so reload ip6h and iaddr in that case alone before the destination-address write; the neutral-map modes never pull and keep their cached pointers.
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Analysis
by VulDB Data Team • 08/10/2026
The vulnerability exists within the Linux kernel's Internet Layer Access (ILA) implementation where a use-after-free condition occurs due to improper handling of IPv6 header pointers following memory reallocation operations. This flaw specifically affects the ila_csum_adjust_transport() function which caches the IPv6 header pointer before invoking pskb_may_pull(), a function that may relocate skb data structures when dealing with non-linear skbs containing transport headers in page fragments. The caching of ip6h pointer creates a dangling reference when pskb_may_pull() executes __pskb_pull_tail() or pskb_expand_head() operations, which subsequently free the original skb head memory while leaving the cached pointer pointing to freed memory.
The technical execution path involves multiple memory management operations that create the conditions for the use-after-free scenario. When pskb_may_pull() processes non-linear skbs with transport headers in page fragments, it performs memory reallocation operations that invalidate previously cached pointers. The function get_csum_diff(ip6h, p) then attempts to read from this freed memory location, creating a potential security risk. Additionally, ila_update_ipv6_locator() reuses the same cached ip6h pointer after the csum-adjust call, further exacerbating the vulnerability by writing new locator information through the dangling pointer reference.
This vulnerability has significant operational impact as it can be exploited remotely through IPv6 packets routed through configured ILA csum-adjust-transport routes or receive-side mappings. The attack requires minimal privileges for configuration since only CAP_NET_ADMIN permissions are needed to establish the vulnerable route or mapping, but once established, any unauthenticated remote attacker can trigger the exploit by sending specially crafted packets. The vulnerability manifests as a slab-use-after-free condition detected by KASAN (Kernel Address Sanitizer), which indicates memory corruption that could potentially lead to privilege escalation or system instability.
The mitigation strategy focuses on proper pointer invalidation and reloading mechanisms following pskb_may_pull() calls. The recommended fix involves reloading the ip6h pointer after each pskb_may_pull() operation in ila_csum_adjust_transport() before performing any csum-diff operations that would read from the header. Furthermore, in ila_update_ipv6_locator(), the solution specifically addresses the ILA_CSUM_ADJUST_TRANSPORT case where skb pulling occurs, requiring reload of both ip6h and iaddr pointers before writing destination-address information. This approach ensures that neutral-map modes which never perform skb pulling operations maintain their cached pointers while only the problematic transport adjustment case receives proper pointer validation.
This vulnerability aligns with CWE-416 (Use After Free) and represents a classic memory safety issue in kernel networking code where pointer invalidation occurs during memory management operations. The ATT&CK framework categorizes this as a privilege escalation technique through kernel memory corruption, potentially enabling attackers to execute arbitrary code with kernel-level privileges. The flaw demonstrates the complexity of maintaining valid pointers in kernel networking code when dealing with non-linear skbs and memory reallocation operations, highlighting the need for careful pointer management in kernel space where such errors can compromise entire system security and stability.