CVE-2026-41676: Rust-openssl Buffer Overflow Vulnerability

CVE-2026-41676 Overview

CVE-2026-41676 is a heap/stack overflow vulnerability in rust-openssl, a library providing OpenSSL bindings for the Rust programming language. The vulnerability exists in versions 0.9.27 to before 0.10.78, where the Deriver::derive and PkeyCtxRef::derive functions improperly handle buffer length validation when interacting with OpenSSL's EVP_PKEY_derive function. This allows memory corruption from otherwise safe Rust code when using older OpenSSL 1.1.x versions.

Critical Impact
Applications using rust-openssl with OpenSSL 1.1.x for X25519, X448, DH, or HKDF-extract operations may experience heap or stack overflow when callers pass undersized buffers, potentially leading to memory corruption, crashes, or code execution.

Affected Products

rust-openssl versions 0.9.27 to 0.10.77
Applications using rust-openssl with OpenSSL 1.1.x
Systems performing X25519, X448, DH, or HKDF-extract key derivation operations

Discovery Timeline

2026-04-24 - CVE CVE-2026-41676 published to NVD
2026-04-28 - Last updated in NVD database

Technical Details for CVE-2026-41676

Vulnerability Analysis

This vulnerability stems from an improper calculation of buffer size (CWE-131) in the rust-openssl library's key derivation implementation. The Deriver::derive and PkeyCtxRef::derive functions set the length parameter to the buffer's length and pass it as both an input and output parameter to OpenSSL's EVP_PKEY_derive function. The implementation relies on OpenSSL to honor this length constraint.

However, in OpenSSL 1.1.x, certain key derivation algorithms—specifically X25519, X448, Diffie-Hellman (DH), and HKDF-extract—ignore the incoming *keylen parameter entirely. Instead, these algorithms unconditionally write the full shared secret to the output buffer (32 bytes for X25519, 56 bytes for X448, or the full prime-size for DH operations).

When a caller passes a buffer slice smaller than the expected output size, OpenSSL writes beyond the allocated buffer boundaries, resulting in a heap or stack overflow depending on where the buffer is allocated. This is particularly dangerous as it violates Rust's memory safety guarantees from code that appears safe.

OpenSSL 3.x providers properly validate buffer lengths, so this vulnerability only impacts systems running older OpenSSL 1.1.x versions.

Root Cause

The root cause is an incorrect calculation of buffer size in the rust-openssl bindings. The library assumes that OpenSSL's EVP_PKEY_derive function will respect the provided buffer length for all algorithms, but OpenSSL 1.1.x implementations of X25519, X448, DH, and HKDF-extract do not honor this constraint. The library fails to pre-validate that the destination buffer is large enough to hold the expected output for these specific algorithms before calling the underlying OpenSSL function.

Attack Vector

The attack vector is network-based, requiring specific conditions to be present. An attacker could potentially exploit this vulnerability by:

Targeting applications that use rust-openssl for cryptographic key derivation
Manipulating inputs that influence the buffer size passed to derivation functions
Triggering key derivation operations with X25519, X448, DH, or HKDF-extract algorithms
Causing the undersized buffer to be overwritten, leading to memory corruption

The vulnerability requires the target system to be running OpenSSL 1.1.x (not 3.x) and using the affected rust-openssl versions for key derivation operations. While no public exploits are currently available, the memory corruption could potentially be leveraged for denial of service or, in some scenarios, arbitrary code execution.

Detection Methods for CVE-2026-41676

Indicators of Compromise

Unexpected application crashes during cryptographic key exchange operations
Memory corruption errors or segmentation faults in Rust applications using OpenSSL bindings
Abnormal memory access patterns in applications performing X25519, X448, DH, or HKDF operations
Core dumps indicating buffer overflows in key derivation code paths

Detection Strategies

Audit application dependencies for rust-openssl versions between 0.9.27 and 0.10.77
Monitor for unexpected crashes or memory errors in applications using rust-openssl
Use memory sanitizers (AddressSanitizer, MemorySanitizer) during testing to detect buffer overflows
Implement runtime monitoring for abnormal memory access in cryptographic operations

Monitoring Recommendations

Enable crash reporting and analysis for production applications using rust-openssl
Monitor system logs for signs of memory corruption or unexpected process terminations
Implement dependency scanning in CI/CD pipelines to detect vulnerable rust-openssl versions
Track OpenSSL version in deployment environments to identify systems running 1.1.x

How to Mitigate CVE-2026-41676

Immediate Actions Required

Update rust-openssl to version 0.10.78 or later immediately
Audit all applications using rust-openssl for vulnerable versions
Consider upgrading to OpenSSL 3.x which properly validates buffer lengths
Run dependency vulnerability scans to identify affected projects

Patch Information

The vulnerability has been fixed in rust-openssl version 0.10.78. Update your Cargo.toml dependency to specify the patched version. For detailed information about the fix and additional guidance, refer to the GitHub Security Advisory GHSA-pqf5-4pqq-29f5.

Workarounds

Upgrade to OpenSSL 3.x which includes proper length validation for affected algorithms
Ensure buffers passed to key derivation functions are sized appropriately for the algorithm (32 bytes for X25519, 56 bytes for X448, prime-size for DH)
Avoid using affected algorithms (X25519, X448, DH, HKDF-extract) until the library is updated
Implement input validation to ensure adequate buffer sizes before calling derivation functions

bash

# Update rust-openssl in Cargo.toml
# Change from vulnerable version:
# openssl = "0.10.77"
# To patched version:
openssl = "0.10.78"

# Then rebuild your project
cargo update -p openssl
cargo build --release