CVE-2023-1255: OpenSSL AES-XTS DoS Vulnerability

CVE-2023-1255 Overview

CVE-2023-1255 is an out-of-bounds read vulnerability in OpenSSL's AES-XTS cipher decryption implementation specifically affecting 64-bit ARM platforms. The bug causes the decryption routine to read past the input buffer under specific ciphertext size conditions, potentially leading to application crashes and denial of service.

The AES-XTS algorithm is commonly used for disk encryption, and this vulnerability affects applications utilizing this cipher mode on ARM64 architecture. The decryption implementation reads past the end of the ciphertext buffer when the ciphertext size is 4 mod 5 in 16-byte blocks (e.g., 144 bytes or 1024 bytes). If the memory region following the ciphertext buffer is unmapped, the out-of-bounds read triggers a crash.

Critical Impact

Applications using AES-XTS decryption on 64-bit ARM platforms can experience denial of service crashes when processing ciphertext of specific sizes, particularly impacting disk encryption systems and security-critical storage applications.

Affected Products

• OpenSSL 3.0.0 through 3.0.8
• OpenSSL 3.1.0
• OpenSSL on 64-bit ARM platforms using AES-XTS cipher

Discovery Timeline

• April 20, 2023 - CVE-2023-1255 published to NVD
• February 4, 2025 - Last updated in NVD database

Technical Details for CVE-2023-1255

Vulnerability Analysis

This vulnerability is classified as CWE-125 (Out-of-Bounds Read), affecting the AES-XTS cipher decryption implementation in OpenSSL when running on 64-bit ARM platforms. The root cause lies in improper bounds checking within the ARM64-optimized assembly code for AES-XTS decryption operations.

The vulnerability requires specific conditions to trigger: the ciphertext size must be congruent to 4 mod 5 when counted in 16-byte blocks. This means ciphertext sizes such as 144 bytes, 1024 bytes, or similar values that meet this mathematical condition can cause the decryption routine to read beyond the allocated buffer boundary.

While the network attack vector indicates remote exploitation potential, the complexity is high due to the specific conditions required. An attacker would need to control both the size and memory location of the ciphertext buffer being processed by the vulnerable application. This makes practical exploitation difficult, though the impact could be significant in environments where disk encryption services are exposed.

Root Cause

The vulnerability stems from a bug in the 64-bit ARM platform-specific implementation of the AES-XTS cipher decryption routine. The assembly code optimized for ARM64 architecture fails to properly validate buffer boundaries when processing ciphertext blocks. Specifically, the loop handling the final blocks of ciphertext does not correctly account for the buffer size when the total size falls into the problematic modulo class, causing the routine to read additional bytes beyond the allocated input buffer.

Attack Vector

An attacker can exploit this vulnerability by causing an application to decrypt ciphertext with a specifically crafted size on a 64-bit ARM platform. The attack scenario involves:

1. Targeting an application that uses OpenSSL's AES-XTS decryption on ARM64 architecture
2. Providing ciphertext with a size that is 4 mod 5 in 16-byte blocks
3. Ensuring the memory following the ciphertext buffer is unmapped

If the attacker can influence the ciphertext input to an affected application—such as through a file encryption service, encrypted storage system, or any network service using AES-XTS—they may cause the application to crash, resulting in denial of service. The vulnerability does not allow for code execution or information disclosure beyond the crash itself.

Detection Methods for CVE-2023-1255

Indicators of Compromise

• Unexpected application crashes on 64-bit ARM systems using OpenSSL for AES-XTS decryption
• Segmentation fault signals (SIGSEGV) in processes linked against vulnerable OpenSSL versions
• Core dumps indicating out-of-bounds memory access in OpenSSL cryptographic operations
• Service interruptions in disk encryption or storage services on ARM64 platforms

Detection Strategies

• Monitor for crash reports and core dumps associated with OpenSSL-linked applications on ARM64 systems
• Implement version detection for OpenSSL libraries to identify vulnerable installations (versions 3.0.0-3.0.8 and 3.1.0)
• Deploy endpoint detection rules to flag repeated crashes in cryptographic services
• Audit application logs for memory access violations during decryption operations

Monitoring Recommendations

• Enable kernel crash monitoring on ARM64 servers running OpenSSL-based services
• Configure alerting for service restarts of disk encryption daemons and storage services
• Monitor memory-related system errors on ARM platforms using security telemetry
• Implement availability monitoring for critical services using AES-XTS encryption

How to Mitigate CVE-2023-1255

Immediate Actions Required

• Upgrade OpenSSL to version 3.0.9 or 3.1.1 or later on all 64-bit ARM systems
• Inventory all ARM64 deployments using OpenSSL for disk encryption or AES-XTS operations
• Apply vendor-provided patches from downstream distributions (Linux, BSD, etc.)
• Prioritize patching for internet-facing services and disk encryption infrastructure

Patch Information

OpenSSL has released patches addressing this vulnerability. The fixes are available in the OpenSSL Git repository with commit 02ac9c9420275868472f33b01def01218742b8bb for the 3.0 branch and commit bc2f61ad70971869b242fc1cb445b98bad50074a for the 3.1 branch.

Users should upgrade to:

• OpenSSL 3.0.9 or later (for 3.0.x branch)
• OpenSSL 3.1.1 or later (for 3.1.x branch)

For detailed information, refer to the OpenSSL Security Advisory and the NetApp Security Advisory for NetApp product-specific guidance.

Workarounds

• Restrict network access to services using AES-XTS decryption on ARM64 platforms until patching is complete
• Implement input validation to reject ciphertext sizes that match the vulnerable pattern (4 mod 5 in 16-byte blocks)
• Consider temporarily switching to non-ARM platforms for critical encryption services if immediate patching is not possible
• Deploy application-level crash recovery mechanisms to minimize service disruption

# Check OpenSSL version on ARM64 systems
openssl version -a

# Verify platform architecture
uname -m

# Update OpenSSL on Debian/Ubuntu ARM64 systems
sudo apt update && sudo apt upgrade openssl libssl3

# Update OpenSSL on RHEL/CentOS ARM64 systems
sudo dnf update openssl