CVE-2026-41678: Rust-openssl Buffer Overflow Vulnerability

CVE-2026-41678 Overview

CVE-2026-41678 is an out-of-bounds write vulnerability in rust-openssl, the OpenSSL bindings for the Rust programming language. The vulnerability exists in the aes::unwrap_key() function, which contains an incorrect assertion that inverts the intended buffer size check. This logic error allows the function to write past the end of the output buffer, causing memory corruption from what is intended to be a safe public function.

Critical Impact

A logic error in buffer size validation allows out-of-bounds writes, potentially leading to memory corruption, crashes, or code execution in applications using the affected aes::unwrap_key() function.

Affected Products

• rust-openssl versions prior to 0.10.78
• Applications using the aes::unwrap_key() function from vulnerable rust-openssl versions
• Rust projects with rust-openssl as a dependency

Discovery Timeline

• 2026-04-24 - CVE-2026-41678 published to NVD
• 2026-04-28 - Last updated in NVD database

Technical Details for CVE-2026-41678

Vulnerability Analysis

This vulnerability stems from a logic error in the aes::unwrap_key() function within rust-openssl. The function is designed to unwrap AES-wrapped keys and includes a buffer size assertion to ensure the output buffer is adequately sized. However, the assertion logic is inverted—it checks that out.len() + 8 <= in_.len() when it should verify out.len() >= in_.len() - 8.

This inverted check has the paradoxical effect of accepting only buffers at or below the minimum required size while rejecting larger, safer buffers. When a smaller-than-required buffer is provided and passes this flawed check, the function proceeds to write beyond the allocated buffer boundaries. The overflow size is calculated as in_.len() - 8 - out.len() bytes, meaning the severity of the overflow directly correlates with how undersized the provided buffer is.

The vulnerability is particularly concerning because it exists in what is exposed as a safe public function in Rust, violating Rust's memory safety guarantees without requiring unsafe code blocks in the calling application.

Root Cause

The root cause is a reversed conditional assertion in the buffer size validation logic. The intended invariant out.len() >= in_.len() - 8 was incorrectly implemented as out.len() + 8 <= in_.len(), which is mathematically equivalent to out.len() <= in_.len() - 8. This subtle but critical error inverts the safety check, causing the function to reject safe inputs and accept unsafe ones.

Attack Vector

The vulnerability is exploitable over the network in scenarios where an attacker can influence the input parameters to the aes::unwrap_key() function. Exploitation requires:

1. An application using rust-openssl versions prior to 0.10.78
2. Application code that calls aes::unwrap_key() with attacker-controllable input
3. A scenario where the output buffer size can be manipulated or is derived from attacker input

When these conditions are met, an attacker can craft inputs that cause out-of-bounds memory writes. The potential impacts include application crashes (denial of service), corruption of adjacent memory structures, and potentially arbitrary code execution depending on memory layout and application context.

The vulnerability mechanism involves incorrect buffer validation logic. When aes::unwrap_key() is called with a buffer that passes the flawed assertion check, the function writes in_.len() - 8 bytes to the output buffer, exceeding its actual capacity. For detailed technical information, refer to the GitHub Security Advisory.

Detection Methods for CVE-2026-41678

Indicators of Compromise

• Application crashes or segmentation faults in code paths involving AES key unwrapping operations
• Memory corruption symptoms in applications using rust-openssl for cryptographic operations
• Unexpected behavior or crashes when processing AES-wrapped key material
• Address Sanitizer (ASan) reports indicating heap buffer overflows in rust-openssl code

Detection Strategies

• Audit Cargo.toml and Cargo.lock files for rust-openssl dependencies with versions below 0.10.78
• Run cargo audit to identify known vulnerabilities in project dependencies
• Use memory sanitizers (ASan, MSan) during testing to detect out-of-bounds writes
• Implement runtime monitoring for applications that process untrusted AES-wrapped keys

Monitoring Recommendations

• Monitor application logs for crash reports related to cryptographic operations
• Set up dependency vulnerability scanning in CI/CD pipelines to catch outdated rust-openssl versions
• Enable crash dump collection and analysis for production applications using this library
• Implement application performance monitoring to detect anomalous memory usage patterns

How to Mitigate CVE-2026-41678

Immediate Actions Required

• Update rust-openssl to version 0.10.78 or later immediately
• Run cargo update -p openssl to update the dependency in existing projects
• Review and rebuild all applications that depend on rust-openssl
• Audit code for usage of the aes::unwrap_key() function to assess exposure

Patch Information

The vulnerability is fixed in rust-openssl version 0.10.78. The patch corrects the assertion logic in aes::unwrap_key() to properly validate that the output buffer is large enough to hold the unwrapped key material. Users should update their Cargo.toml to require at minimum version 0.10.78 of the openssl crate.

For complete patch details, refer to the GitHub Security Advisory.

Workarounds

• If immediate patching is not possible, avoid using the aes::unwrap_key() function until the update can be applied
• Implement input validation at the application level to ensure output buffers are always adequately sized
• Consider using alternative AES key unwrapping implementations temporarily
• Restrict network exposure of applications that process AES-wrapped keys from untrusted sources

# Update rust-openssl to patched version
cargo update -p openssl

# Verify the updated version
cargo tree -p openssl

# Ensure Cargo.toml specifies minimum safe version
# openssl = ">=0.10.78"