Cryptography is all about keeping secrets safe. But, when the software you trust for encryption has a flaw, everything can fall apart. In this long-form post, we'll explore CVE-2022-29242—a real-world vulnerability that affected the GOST crypto engine, a reference implementation for Russian government-approved cryptography (GOST algorithms) in OpenSSL.

We'll break things down in plain language, look at actual code, and share tips on protecting your systems. Whether you're a security professional or just curious about crypto, you'll find solid info here you can't get elsewhere.

What Is the GOST Engine?

The GOST engine brings support for the GOST cryptographic algorithms) to OpenSSL, a hugely popular open-source encryption toolkit. It's particularly required in Russian government and business projects, using ciphers like:

Magma (block cipher)

If you use OpenSSL and work in Russia or with Russian standards, it's likely you or your customers rely on the GOST engine.

In Simple Terms

CVE-2022-29242 is a buffer overflow bug. If your OpenSSL is set up with the GOST engine, and you’re using one particular cipher (TLS_GOSTR341112_256_WITH_KUZNYECHIK_CTR_OMAC), and the server submits a 512-bit GOST secret key, an attacker can trigger a buffer overflow.

The Details

- Affected product: GOST Engine for OpenSSL

Attack vector: Server uses 512-bit GOST secret keys

When these things line up, the engine doesn’t check input sizes correctly. That means a carefully crafted network payload can overwrite parts of memory—the heart of a buffer overflow.

Why Buffer Overflows Matter

Buffer overflows are one of those "classic" security bugs. When software writes past the end of an allocated memory space ("buffer"), it can:

Allow data to be leaked or modified

With cryptographic code, a buffer overflow is especially bad. An attacker could hijack secure connections, steal keys, or cause denial-of-service.

A Simple Explanation

1. Handshake: The TLS client and server agree to use TLS_GOSTR341112_256_WITH_KUZNYECHIK_CTR_OMAC.

GOST engine processes the key—but without sufficient size checks.

4. BOOM: The oversized input overwrites memory, letting an attacker take over the process or crash it.

Here's a simplified snippet from vulnerable code (not real GOST code, but representative)

#define MAX_KEY_SIZE 64 // supposedly max

void process_server_key(const unsigned char *key, size_t keylen) {
    unsigned char buf[MAX_KEY_SIZE];

    // vulnerable: no bounds check!
    memcpy(buf, key, keylen);

    // ...rest of processing...
}

If keylen is 128 bytes (for a 1024-bit key), memcpy will overflow buf (only 64 bytes!).

The Real Engine Fix

The real fix in GOST engine 3..1 is to add bounds checking before copying the key.

*Patched code (simplified):*

if (keylen > MAX_KEY_SIZE) {
    // Error: key too big!
    return ERROR;
}
memcpy(buf, key, keylen);

Only the specific cipher (TLS_GOSTR341112_256_WITH_KUZNYECHIK_CTR_OMAC) is affected.

- Common OpenSSL configurations might be vulnerable out of the box if the GOST engine is enabled and that cipher is supported.
- Default key sizes aren’t vulnerable—only when an abnormally large (512-bit) secret is used by the server.

Crash the client connecting to the vulnerable server

- Potentially allow remote code execution on the client, depending on other protections (ASLR, stack guards, etc.)

Connected custom or regular clients will overflow their local memory and potentially be compromised.

Public exploits:
Currently, there are no public working exploits for this specific bug, likely because the scenario is rare (unusual key size and cipher), but proof-of-concept code could be crafted based on the description above.

1. Upgrade the GOST Engine

Always update!
Upgrade to version 3..1 or later of the GOST engine. This removes the vulnerability.

If you can’t upgrade immediately, disable the vulnerable cipher

- Remove/disable TLS_GOSTR341112_256_WITH_KUZNYECHIK_CTR_OMAC from your TLS configuration.

- In OpenSSL config, restrict supported ciphers

CipherString = DEFAULT:!TLS_GOSTR341112_256_WITH_KUZNYECHIK_CTR_OMAC

Keep OpenSSL and all crypto engines up-to-date.

- Always apply security best practices: limit connections, monitor for crashes, enable ASLR, and use stack protections.

- Original CVE Record at NIST
- GOST Engine GitHub (Official)
- GOST engine 3..1 Release Notes & Patch
- GOST Engine Commit Fix
- Wikipedia: GOST)

Conclusion

CVE-2022-29242 is a great reminder how even modern crypto projects can have classic bugs like buffer overflows—sometimes in obscure, country-specific algorithms. If your projects or clients ever touch Russian cryptography or OpenSSL’s GOST engine, check your versions now.

Timeline

Published on: 05/24/2022 15:15:00 UTC
Last modified on: 06/07/2022 16:54:00 UTC