CVE-2025-5222: ICU Buffer Overflow Vulnerability

CVE-2025-5222 Overview

A stack buffer overflow vulnerability was discovered in International Components for Unicode (ICU), a widely-used library that provides Unicode and globalization support for software applications. The vulnerability occurs when running the genrb binary, where the subtag struct overflows at the SRBRoot::addTag function. This memory corruption issue can potentially lead to local arbitrary code execution when processing maliciously crafted input.

Critical Impact

This stack buffer overflow vulnerability enables local arbitrary code execution through memory corruption, requiring user interaction to exploit but potentially allowing complete system compromise.

Affected Products

• Unicode International Components for Unicode (ICU)
• Linux distributions using ICU (Red Hat, Debian, and derivatives)
• Applications and services that depend on ICU for internationalization support

Discovery Timeline

• May 27, 2025 - CVE-2025-5222 published to NVD
• August 8, 2025 - Last updated in NVD database

Technical Details for CVE-2025-5222

Vulnerability Analysis

This vulnerability is classified as CWE-120 (Buffer Copy without Checking Size of Input), commonly known as a classic buffer overflow. The issue resides in the resource bundle generation tool (genrb) that is part of the ICU library suite. When processing resource bundle data, the SRBRoot::addTag function fails to properly validate the size of input being copied into the subtag structure, allowing an attacker to overflow the stack-allocated buffer.

The local attack vector combined with the requirement for user interaction means that exploitation typically requires social engineering to convince a user to process a malicious resource bundle file. However, successful exploitation can result in complete compromise of confidentiality, integrity, and availability on the affected system.

Root Cause

The root cause is insufficient bounds checking in the SRBRoot::addTag function when handling subtag data during resource bundle generation. The function copies data into a fixed-size stack buffer without validating that the input size does not exceed the buffer's capacity. This allows specially crafted input to write beyond the allocated stack space, corrupting adjacent memory including return addresses and saved registers.

Attack Vector

The attack requires local access and user interaction to exploit. An attacker would need to craft a malicious resource bundle file and convince a user or automated process to run the genrb binary against it. The exploitation complexity is high due to the need to carefully construct the overflow to achieve code execution while bypassing any stack protection mechanisms that may be in place.

The vulnerability manifests when the genrb tool processes the malicious input, causing the subtag struct to overflow during tag processing. This stack corruption can be leveraged to hijack program control flow and execute arbitrary code with the privileges of the user running the tool. For detailed technical analysis, refer to the Red Hat Bugzilla Report #2368600.

Detection Methods for CVE-2025-5222

Indicators of Compromise

• Unexpected crashes or core dumps from the genrb binary
• Anomalous resource bundle files with unusually large or malformed subtag sections
• Evidence of memory corruption in process logs or crash reports
• Suspicious execution of genrb with untrusted input files

Detection Strategies

• Monitor for abnormal behavior from ICU-related binaries, particularly genrb
• Implement file integrity monitoring on ICU library files and binaries
• Use endpoint detection and response (EDR) solutions to detect memory corruption attempts
• Deploy SentinelOne Singularity to identify and block exploitation attempts in real-time

Monitoring Recommendations

• Enable stack canary and address space layout randomization (ASLR) violation alerts
• Log and audit all executions of the genrb binary with external input
• Monitor for unusual process spawning patterns following ICU tool execution
• Implement security information and event management (SIEM) rules for buffer overflow indicators

How to Mitigate CVE-2025-5222

Immediate Actions Required

• Update ICU to the latest patched version as provided by your Linux distribution
• Review systems for any automated processes that invoke genrb with external input
• Restrict access to the genrb binary to trusted users only
• Apply vendor security patches immediately for Red Hat and Debian-based systems

Patch Information

Multiple Linux distributions have released security advisories and patches addressing this vulnerability:

• Red Hat Security Advisory RHSA-2025:11888
• Red Hat Security Advisory RHSA-2025:12083
• Red Hat Security Advisory RHSA-2025:12331
• Red Hat Security Advisory RHSA-2025:12332
• Red Hat Security Advisory RHSA-2025:12333
• Debian LTS Announcement June 2025

For additional details, see the Red Hat CVE-2025-5222 Reference.

Workarounds

• Avoid running genrb with untrusted or externally-sourced resource bundle files
• Use containerization or sandboxing when processing resource bundles from unknown sources
• Implement strict input validation for any workflows involving ICU resource bundle generation
• Consider disabling or removing the genrb binary if resource bundle generation is not required

# Check installed ICU version
icu-config --version

# Update ICU on Red Hat-based systems
sudo dnf update icu

# Update ICU on Debian-based systems
sudo apt update && sudo apt upgrade icu-devtools libicu-dev

# Restrict access to genrb binary as temporary mitigation
sudo chmod 750 /usr/bin/genrb