CVE-2026-74550 in Linux
Summary
by MITRE • 08/15/2026
In the Linux kernel, the following vulnerability has been resolved:
net: do not send ICMP/NDISC Redirects when peer allocation fails
When inet_getpeer_v4() or inet_getpeer_v6() fails to allocate a peer entry under memory pressure or tree size caps, redirect handlers previously fell back to sending un-rate-limited ICMP/NDISC Redirect messages.
In IPv4, ip_rt_send_redirect() called icmp_send() directly when peer == NULL. In IPv6, ip6_forward() and ndisc_send_redirect() passed a NULL peer into inet_peer_xrlim_allow(), which returned true when peer == NULL.
Because ICMP/NDISC Redirects are not part of the default global rate limit mask (sysctl_icmp_ratemask), sending redirects when peer == NULL creates an un-rate-limited ICMP packet storm.
Fix this by failing closed in ip_rt_send_redirect(), ip6_forward(), and ndisc_send_redirect() when peer is NULL.
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Analysis
by VulDB Data Team • 08/15/2026
This vulnerability resides in the Linux kernel's network stack implementation where improper handling of peer allocation failures leads to potential denial of service through uncontrolled ICMP and neighbor discovery redirects. The issue stems from the kernel's routing subsystem where the inet_getpeer_v4() and inet_getpeer_v6() functions are responsible for managing peer entries in the routing tables. When memory pressure or tree size limits are reached, these functions fail to allocate new peer entries, yet the redirect handling code paths do not properly account for this failure condition.
The technical flaw manifests when the kernel attempts to send ICMP redirects or neighbor discovery redirects without proper validation of peer entry availability. In IPv4 implementations, the ip_rt_send_redirect() function directly invokes icmp_send() when the peer parameter equals NULL, bypassing normal rate limiting mechanisms that typically protect against redirect storms. Similarly, in IPv6 implementations, both ip6_forward() and ndisc_send_redirect() functions pass NULL peer entries to inet_peer_xrlim_allow(), which incorrectly returns true for null peers, effectively disabling rate limiting controls. This behavior creates a critical security gap where malicious actors can exploit memory pressure conditions to flood network infrastructure with unlimited redirect messages.
The operational impact of this vulnerability is severe as it enables attackers to trigger resource exhaustion through ICMP packet storms that bypass standard rate limiting mechanisms. Since ICMP/NDISC redirects are not included in the default global rate limit mask controlled by sysctl_icmp_ratemask, the system becomes vulnerable to sustained flooding attacks that can consume network bandwidth and processing resources. The vulnerability affects both IPv4 and IPv6 implementations, making it particularly dangerous in modern network environments where dual-stack configurations are common.
From a cybersecurity perspective, this vulnerability aligns with CWE-362: Concurrent Execution using Shared Resource with Improper Synchronization and CWE-770: Allocation of Resources Without Limits or Throttling. The fix implements proper error handling by failing closed in the redirect functions when peer allocation fails, preventing the transmission of redirects under invalid conditions. This approach directly addresses ATT&CK technique T1498.001: Network Denial of Service through resource exhaustion attacks. The mitigation strategy requires updating the kernel to ensure that ip_rt_send_redirect(), ip6_forward(), and ndisc_send_redirect() functions return immediately when peer entries are unavailable, effectively closing the security gap in the routing subsystem's redirect handling code paths.