CVE-2025-0624: GRUB2 Network Boot RCE Vulnerability

CVE-2025-0624 Overview

CVE-2025-0624 is an out-of-bounds write vulnerability in GRUB2, the GNU GRand Unified Bootloader used by most Linux distributions. The flaw lives in the network boot code path, where grub_strcpy() copies data from a user-controlled environment variable into an internal buffer without accounting for the variable's length. An attacker positioned on the same network segment as the booting system can craft network responses that overflow the buffer during configuration file lookup. Successful exploitation can lead to remote code execution in the pre-boot environment and bypass of Secure Boot protections. The issue is tracked as [CWE-787] (Out-of-bounds Write) and affects GRUB2 builds shipped across multiple Red Hat Enterprise Linux releases and NetApp products.

Critical Impact
Adjacent-network attackers can corrupt GRUB2 memory during PXE boot, achieve pre-OS code execution, and bypass Secure Boot — compromising the chain of trust before the operating system loads.

Affected Products

GRUB2 (upstream) network boot module
Red Hat Enterprise Linux distributions shipping affected GRUB2 builds (RHSA-2025:2521, RHSA-2025:2653, RHSA-2025:7702 and related advisories)
NetApp products referenced in advisory NTAP-20250516-0006

Discovery Timeline

2025-02-19 - CVE-2025-0624 published to the National Vulnerability Database
2026-04-15 - Last updated in NVD database

Technical Details for CVE-2025-0624

Vulnerability Analysis

The vulnerability resides in the GRUB2 network boot logic responsible for locating the bootloader's configuration file. When GRUB2 boots over the network via PXE or similar transports, it constructs file paths and search expressions using values pulled from environment variables. One of these variables is attacker-influenced because its content is derived from data delivered through the network boot exchange.

GRUB2 passes the attacker-influenced string into grub_strcpy(), which performs an unbounded copy into a fixed-size internal buffer. Because the destination buffer is sized without first measuring the source string, a long environment variable value writes past the buffer boundary and corrupts adjacent memory in the GRUB2 runtime.

Exploitation occurs before the operating system kernel loads, so platform-level mitigations such as kernel ASLR, SELinux, or endpoint agents are not yet active. Memory corruption at this stage enables an attacker to subvert the Secure Boot trust chain by hijacking execution inside a signed bootloader.

Root Cause

The root cause is missing length validation before invoking grub_strcpy(). GRUB2 trusts the environment variable contents implicitly and allocates an internal buffer without sizing it against the actual source length, producing a classic [CWE-787] out-of-bounds write.

Attack Vector

The attack vector is adjacent network: the attacker must reach the target's network boot segment, for example by operating a rogue DHCP, TFTP, or HTTP boot server, or by intercepting legitimate PXE traffic. The attacker supplies a crafted environment variable value that GRUB2 consumes when searching for its configuration file, triggering the overflow during the pre-boot phase.

No verified public proof-of-concept code is available at the time of writing. Refer to the Red Hat CVE Report for CVE-2025-0624 and the Red Hat Bugzilla entry #2346112 for upstream technical details.

Detection Methods for CVE-2025-0624

Indicators of Compromise

Unexpected DHCP, TFTP, or HTTP boot servers responding on segments where PXE boot is performed.
Abnormally long or malformed values in PXE-delivered boot file names, next-server fields, or DHCP option 209/210 entries.
GRUB2 boot failures, unexpected reboots, or shell drops on network-booted systems immediately after firmware hand-off.

Detection Strategies

Inventory all systems that perform network boot and verify the installed grub2 package version against the fixed builds listed in the Red Hat advisories.
Capture and inspect PXE/TFTP traffic for oversized configuration paths or environment variable strings sourced from non-authorized servers.
Monitor Secure Boot measurement logs (TPM event log, PCR values) for deviations from a known-good baseline on network-booted hosts.

Monitoring Recommendations

Alert on new MAC or IP addresses offering DHCP or TFTP services on VLANs that host PXE clients.
Forward bootloader and firmware logs to a centralized log platform for retention and correlation with network telemetry.
Track package update compliance for grub2, grub2-efi, and shim across the fleet using configuration management tooling.

How to Mitigate CVE-2025-0624

Immediate Actions Required

Apply vendor patches from the relevant Red Hat advisories, including RHSA-2025:2521, RHSA-2025:2653, RHSA-2025:7702, and the NetApp advisory NTAP-20250516-0006.
Restrict PXE/TFTP services to dedicated, isolated provisioning VLANs and disable network boot on systems that do not require it.
Enforce authenticated boot transports (HTTPS boot, signed configuration files) where supported by firmware and infrastructure.

Patch Information

Red Hat has published more than a dozen errata addressing CVE-2025-0624 across RHEL streams. Representative advisories include RHSA-2025:2521, RHSA-2025:2655, RHSA-2025:2784, RHSA-2025:3297, RHSA-2025:3573, RHSA-2025:4422, and RHSA-2025:7702. After updating grub2, regenerate the bootloader configuration and validate Secure Boot enrollment so the new, signed binaries are used on next boot.

Workarounds

Disable network boot in firmware (UEFI/BIOS) on systems that do not require PXE provisioning until patches can be applied.
Segment provisioning networks with strict ACLs so only authorized DHCP, TFTP, and HTTP boot servers can reach booting clients.
Use 802.1X or MACsec on provisioning VLANs to prevent rogue devices from injecting crafted boot responses.

bash

# Example: confirm the installed grub2 package includes the CVE-2025-0624 fix
rpm -q --changelog grub2 | grep -i CVE-2025-0624

# Example: temporarily disable PXE boot via efibootmgr until patching completes
efibootmgr | grep -i -E 'PXE|Network'
efibootmgr -b <BootNNNN> -A   # deactivate the network boot entry