Zephyr Project up to 4.4.x DHCPv4 Client dhcpv4.c dhcpv4_start_internal random values

Summaryinfo

A vulnerability labeled as problematic has been found in Zephyr Project Zephyr up to 4.4.x. This affects the function dhcpv4_start_internal of the file subsys/net/lib/dhcpv4/dhcpv4.c of the component DHCPv4 Client. Executing a manipulation can lead to random values. This vulnerability is handled as CVE-2026-79980. The attack can be executed remotely. There is not any exploit available. The affected component should be upgraded.

Detailsinfo

A vulnerability classified as problematic was found in Zephyr Project Zephyr up to 4.4.x. This vulnerability affects the function dhcpv4_start_internal of the file subsys/net/lib/dhcpv4/dhcpv4.c of the component DHCPv4 Client. The manipulation with an unknown input leads to a random values vulnerability. The CWE definition for the vulnerability is CWE-330. The product uses insufficiently random numbers or values in a security context that depends on unpredictable numbers. As an impact it is known to affect confidentiality. CVE summarizes:

The DHCPv4 client in subsys/net/lib/dhcpv4/dhcpv4.c maintained its transaction identifier (iface->config.dhcpv4.xid) as a counter rather than as a per-transaction random value. It was seeded once with sys_rand32_get() in dhcpv4_start_internal(), incremented by one in dhcpv4_send_discover() and dhcpv4_send_decline(), and never changed by dhcpv4_send_request() — so every RENEWING and REBINDING exchange reused, unchanged, the identifier that had already appeared on the wire in the broadcast DHCPDISCOVER at boot, and where the identifier did move it moved predictably by one. RFC 2131 4.1 requires a single identifier per transaction, chosen so that clients are unlikely to collide. This identifier is the client's only unpredictable reply-validation token. net_dhcpv4_input() accepts a BOOTP reply on op, a matching xid, and a matching chaddr (the interface MAC, which is public); the UDP callback is registered with a wildcard remote address and port, and no server-identifier or source-address check is applied. An attacker who learns one identifier — for example any host on the same segment that sees the broadcast DHCPDISCOVER, or a DHCP server or relay on a network the device previously joined — therefore retains a valid token for the device's whole uptime, and can predict the identifiers of later exchanges, without having to observe the unicast renew traffic or race the legitimate server. A forged reply that passes those checks has effect regardless of client state, because dhcpv4_parse_options() applies its side effects before the state machine gate in dhcpv4_handle_reply(): the router option calls net_if_ipv4_set_gw() and the DNS option calls dns_resolve_reconfigure(). A single accepted datagram can thus repoint the device's default gateway and resolvers at attacker-controlled addresses, redirecting its traffic; during RENEWING or REBINDING a forged DHCPACK re-binds the lease with attacker-chosen parameters and a forged DHCPNAK removes the address and restarts configuration. The fix draws a fresh sys_rand32_get() value at each point where a transaction begins — entering SELECTING, RENEWING and REBINDING, and at the INIT/INIT-REBOOT entry taken when an interface with a lease goes down — while REQUESTING and DECLINE keep the identifier of the exchange they belong to, as RFC 2131 requires. As a side effect the client also no longer discards a slow server's offer after retransmitting a discover, and the initial-discover backoff now draws its own randomness instead of deriving it from the identifier.

The advisory is shared for download at github.com. This vulnerability was named CVE-2026-79980 since 08/25/2026. The exploitation appears to be difficult. The attack can be initiated remotely. No form of authentication is required for a successful exploitation. There are known technical details, but no exploit is available. The MITRE ATT&CK project declares the attack technique as T1600.001.

Upgrading to version 4.5.0 eliminates this vulnerability.

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Productinfo

Type

• Project Management Software

Vendor

• Zephyr Project

Name

• Zephyr

Version

• 4.0
• 4.1
• 4.2
• 4.3
• 4.4

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CPE 2.2info

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