CVE-2026-98485: netfilter: ip6t_rt: fix zero-address non-strict match out-of-bounds read
In the Linux kernel, the following vulnerability has been resolved:
netfilter: ip6trt: fix zero-address non-strict match out-of-bounds read
rtmt6check() permits rules to be configured with rtinfo->addrnr == 0 even when address matching (IP6TRTFSTMASK) is requested.
In the IP6TRTFSTNSTRICT path, rtmt6() evaluates packet routing addresses against rtinfo->addrs[i] and terminates backwards at the bottom of the loop:
if (ipv6addrequal(ap, &rtinfo->addrs[i])) { i++; } if (i == rtinfo->addrnr) break;
When addrnr is 0, if the first packet address matches rtinfo->addrs[0], i is incremented to 1. Because i is now strictly greater than addrnr (0), the loop termination condition (i == rtinfo->addrnr) is bypassed and will never be satisfied.
If a crafted IPv6 packet contains matching routing addresses, i will advance past IP6TRTHOPS (16). The subsequent call to ipv6addrequal() reads beyond struct ip6trt, triggering UBSAN/KASAN out-of-bounds warnings or kernel panics.
Fix this by: 1. Rejecting rules in rtmt6check() where IP6TRTFSTMASK is set but rtinfo->addrnr is zero. 2. In rtmt6(), moving the termination condition (i < rtinfo->addrnr) into the for-loop header condition and removing the backwards break at the end of the loop body.
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
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Fixed in 6.6.159.1-1 - Upgrade
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azurelinux/kernelto a version that resolves this vulnerability.Fixed in 6.6.159.1-1 - Upgrade
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ubuntu/linux-hwe-7.0to a version that resolves this vulnerability.Fixed in 7.0.0-42.42~24.04.1 - Upgrade
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ubuntu/linuxto a version that resolves this vulnerability.Fixed in 7.0.0-42.42 - Upgrade
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ubuntu/linux-awsto a version that resolves this vulnerability.Fixed in 7.0.0-1016.17 - Upgrade
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ubuntu/linux-gcpto a version that resolves this vulnerability.Fixed in 7.0.0-1016.18 - Upgrade
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ubuntu/linux-ibmto a version that resolves this vulnerability.Fixed in 7.0.0-1017.17 - Upgrade
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ubuntu/linux-oem-7.0to a version that resolves this vulnerability.Fixed in 7.0.0-1017.17 - Upgrade
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ubuntu/linux-oracleto a version that resolves this vulnerability.Fixed in 7.0.0-1015.16 - Upgrade
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ubuntu/linux-riscvto a version that resolves this vulnerability.Fixed in 7.0.0-42.42.1 - Compensating control
In rt_mt6_check(), reject rules when IP6T_RT_FST_MASK is set but rtinfo->addrnr is zero.
- Compensating control
In rt_mt6(), move the termination condition i < rtinfo->addrnr into the for-loop header and remove the backwards break at the end of the loop body.
Event History
Frequently Asked Questions
Which systems are exposed to this issue?
Systems are exposed when they use the Linux kernel ip6t_rt matching code and have a rule that requests address matching with IP6T_RT_FST_MASK set while its addrnr value is zero. The vulnerable path is specifically the non-strict IP6T_RT_FST_NSTRICT matching path.
What is required to trigger the out-of-bounds read?
A crafted IPv6 packet must contain routing addresses that match the rule's address entries. When the first routing address matches addrs[0] while addrnr is zero, the loop can continue past IP6T_RT_HOPS (16), causing reads beyond the ip6t_rt structure and potentially UBSAN/KASAN warnings or a kernel panic.
What can be done before a kernel update is available?
Do not permit or retain ip6t_rt rules that request address matching with IP6T_RT_FST_MASK while addrnr is zero. Review existing relevant rules for that combination and remove or correct any such rule.
How can I determine whether a system has the risky rule configuration?
Inspect ip6t_rt rule configuration for rules with IP6T_RT_FST_MASK enabled and addrnr set to zero, particularly those using non-strict matching. Kernel UBSAN or KASAN out-of-bounds reports, or panics while processing matching IPv6 routing-address packets, are also indicators that the vulnerable path may have been reached.