CVE-2026-41677: Rust-openssl Buffer Overflow Vulnerability

CVE-2026-41677 Overview

CVE-2026-41677 is an Out-of-Bounds Read vulnerability affecting rust-openssl, a library that provides OpenSSL bindings for the Rust programming language. The vulnerability exists in the *_from_pem_callback APIs, which fail to properly validate the length value returned by user-supplied password callbacks. When a callback returns a length larger than the allocated buffer, certain versions of OpenSSL may over-read from the buffer, potentially exposing sensitive memory contents.

Critical Impact

Improper callback length validation allows potential memory over-read in OpenSSL versions prior to 3.x, which could lead to information disclosure or application instability.

Affected Products

• rust-openssl versions 0.9.0 to before 0.10.78
• Applications using *_from_pem_callback APIs with custom password callbacks
• Systems running OpenSSL versions prior to 3.x (OpenSSL 3.x is not affected)

Discovery Timeline

• 2026-04-24 - CVE CVE-2026-41677 published to NVD
• 2026-04-28 - Last updated in NVD database

Technical Details for CVE-2026-41677

Vulnerability Analysis

The vulnerability resides in how rust-openssl handles password callback functions used during PEM parsing operations. The *_from_pem_callback family of APIs allows users to provide custom callback functions that supply passwords for encrypted PEM files. These callbacks are expected to return the length of the password they write into a provided buffer.

However, rust-openssl versions from 0.9.0 to before 0.10.78 do not validate whether the returned length exceeds the actual buffer size. When a malformed or malicious callback returns a length greater than the buffer capacity, OpenSSL (in versions prior to 3.x) may read beyond the buffer boundaries when processing the password data.

This Out-of-Bounds Read (CWE-125) could potentially expose adjacent memory contents, though the practical exploitability depends on the specific OpenSSL version in use and the application's memory layout. OpenSSL 3.x includes additional safety checks that prevent this over-read behavior, making systems using OpenSSL 3.x immune to this particular vulnerability.

Root Cause

The root cause is insufficient input validation in the rust-openssl bindings when handling the return value from user-provided password callbacks. The library trusts the callback to return a valid length value without verifying it against the actual buffer size that was passed to the callback. This missing bounds check violates the principle of defense in depth, as it relies entirely on the callback implementation to behave correctly.

Attack Vector

Exploitation requires an attacker to influence the behavior of a password callback function, either by:

1. Providing a malicious callback directly in code they control
2. Exploiting another vulnerability that allows manipulation of callback return values
3. Supply chain attacks where a malicious dependency provides faulty callbacks

The attack is network-accessible as the PEM parsing operations may be triggered by remote data, though successful exploitation requires the application to use vulnerable callback patterns with OpenSSL versions prior to 3.x.

The vulnerability mechanism involves the password callback returning a length value that exceeds the buffer bounds, causing OpenSSL to over-read memory when processing the supposed password data. For detailed technical information, see the GitHub Security Advisory.

Detection Methods for CVE-2026-41677

Indicators of Compromise

• Application crashes or unexpected behavior during PEM file parsing operations
• Memory access violations or segmentation faults in OpenSSL-related code paths
• Unusual memory patterns or data appearing in logs from password-protected PEM operations
• AddressSanitizer (ASan) reports of heap-buffer-overflow reads in affected code paths

Detection Strategies

• Audit dependencies using cargo audit to identify vulnerable rust-openssl versions in your Rust projects
• Review application code for usage of *_from_pem_callback APIs with custom password callbacks
• Implement runtime memory checking tools (ASan, MSan) during testing to detect out-of-bounds reads
• Monitor for applications linked against rust-openssl versions 0.9.0 through 0.10.77

Monitoring Recommendations

• Enable verbose logging for cryptographic operations to detect anomalous PEM parsing behavior
• Deploy application performance monitoring to detect unusual memory access patterns
• Establish alerting for application crashes related to OpenSSL operations
• Conduct regular dependency audits using automated security scanning tools

How to Mitigate CVE-2026-41677

Immediate Actions Required

• Upgrade rust-openssl to version 0.10.78 or later immediately
• Audit all custom password callback implementations for proper length validation
• Consider upgrading to OpenSSL 3.x which is not affected by this vulnerability
• Review supply chain dependencies that may include vulnerable rust-openssl versions

Patch Information

The vulnerability is fixed in rust-openssl version 0.10.78. Update your Cargo.toml to specify the minimum secure version:

[dependencies]
openssl = ">=0.10.78"

For detailed information about the fix, refer to the rust-openssl Security Advisory.

Workarounds

• Upgrade to OpenSSL 3.x, which includes additional safety checks that prevent the over-read behavior
• Implement explicit length validation in all custom password callbacks before returning
• Avoid using *_from_pem_callback APIs with untrusted or dynamically-generated callbacks
• Consider using alternative PEM loading methods that don't rely on user callbacks where possible

# Update rust-openssl in your Cargo project
cargo update -p openssl --precise 0.10.78

# Verify the installed version
cargo tree -p openssl

# Run cargo audit to check for remaining vulnerabilities
cargo audit