Know every vulnerabilitybefore it knows you.
DevGuard continuously monitors your dependencies and alerts you when CVEs like this one affect your stack — with real-time threat intelligence built for developers.
OSEC-2026-02
No affected components available
Background
Mirage's implementation of the ARP protocol (RFC826) caches ARP replies to construct an IPv4 address -> MAC address cache. This cache is long-lived (effectively global), and also contains pending ARP requests, which are replaced by the reply, or deleted after a timeout. ARP replies that do not match any entry in the ARP cache are ignored (dropped).
The maximum amount of memory that a Solo5 unikernel can be assigned is 4GiB (see X86_GUEST_MAX_SIZE and AARCH64_MMIO_BASE).
Problem description
There are no no size constraints on the cache, and with 2^32 IPv4 addresses, it can exceed the maximum amount of memory that can be allocated by a unikernel if an attacker has Layer-2 access to that unikernel and can spoof arbitrary IP addresses. An attacker also needs to trick the unikernel into sending out an ARP query (ARP replies that don't have a corresponding Pending or Dynamic entry in the ARP table are ignored), this can be done by spoofing an ICMP echo request for example. However while attempting to develop an exploit for this another vulnerability was discovered (reported separately).
Impact
All versions of 'arp' are affected, and this module is typically used by a unikernel that provides network services. An affected unikernel can crash with an Out of memory condition. Unikernels that do not have network devices are not affected.
Workaround
Devices on the same network/bridge as a unikernel should have firewall rules (on their TAP devices) that prevent sending ARP packets with IPv4 addresses that the unikernel doesn't own (although this becomes difficult to enforce if DHCP is used).
Unikernel orchestrators can be configured to restart unikernels on crash, although you'd still lose any state that was in memory.
Solution
Use a cache with a fixed upper bound on size, e.g. a LRU cache that drops old entries.
Timeline
2025-05-23: issue discovered by Edwin Török while reviewing code to debug another OOM crash as part of the HACKSAT25 challenge 2025-05-28: issue reported to security@mirage.io 2025-10-20: arp 4.1.0 was released 2026-02-18: security advisory was published
The vulnerability can be exploited over a local network, such as Wi-Fi. It is easy for an attacker to exploit this vulnerability. An attacker does not need any special privileges or access rights. No user interaction is needed for the attacker to exploit this vulnerability. The vulnerability can affect other systems as well, not just the initial system. There is a high impact on the availability of the system.
Exploitation attempts have been detected. Elevated vigilance and prompt remediation are advised.
Probability that this vulnerability will be exploited in the wild within the next 30 days.
We did not find any exploit available. Neither in GitHub repositories nor in the Exploit-Database.
Browse More
Continuously monitor your dependencies and get alerted when vulnerabilities like this one affect your stack.
Checkout DevGuard