# GHSA-m9c9-mc2h-9wjw: Lodestar snappy checksum issue

> Lodestar fails to verify snappy checksums, allowing attackers to cause permanent chain splits and network partitions requiring hard forks.

- **Severity:** Not scored
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 14 Jan 2025

## What is GHSA-m9c9-mc2h-9wjw?

GHSA-m9c9-mc2h-9wjw is a vulnerability in @lodestar/reqresp, published on 14 Jan 2025. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

### Impact
Unintended permanent chain split affecting greater than or equal to 25% of the network, requiring hard fork (network partition requiring hard fork)

Lodestar does not verify checksum in snappy framing uncompressed chunks.

### Vulnerability Details
In Req/Resp protocol the messages are encoded by using ssz_snappy encoding, which is a snappy framing compression over ssz encoded message.

In snappy framing format there are uncompressed chunks, each such chunk is prefixed with a checksum.

Let's see how golang implementation parses such chunks - https://github.com/golang/snappy/blob/master/decode.go#L176

```
	case chunkTypeUncompressedData:
			// Section 4.3. Uncompressed data (chunk type 0x01).
			if chunkLen < checksumSize {
				r.err = ErrCorrupt
				return r.err
			}
			buf := r.buf[:checksumSize]
			if !r.readFull(buf, false) {
				return r.err
			}
			checksum := uint32(buf[0]) | uint32(buf[1])<<8 | uint32(buf[2])<<16 | uint32(buf[3])<<24
			// Read directly into r.decoded instead of via r.buf.
			n := chunkLen - checksumSize
			if n > len(r.decoded) {
				r.err = ErrCorrupt
				return r.err
			}
			if !r.readFull(r.decoded[:n], false) {
				return r.err
			}
			if crc(r.decoded[:n]) != checksum {
				r.err = ErrCorrupt
				return r.err
			}
			r.i, r.j = 0, n
			continue
```

As you can see, if checksum is incorrect, decoder fails and returns error.

Now let's look at lodestar decoder https://github.com/ChainSafe/lodestar/blob/unstable/packages/reqresp/src/encodingStrategies/sszSnappy/snappyFrames/uncompress.ts#L17

```
uncompress(chunk: Uint8ArrayList): Uint8ArrayList | null {
    this.buffer.append(chunk);
    const result = new Uint8ArrayList();
    while (this.buffer.length > 0) {
      if (this.buffer.length < 4) break;

      const type = getChunkType(this.buffer.get(0));
      const frameSize = getFrameSize(this.buffer, 1);

      if (this.buffer.length - 4 < frameSize) {
        break;
      }

      const data = this.buffer.subarray(4, 4 + frameSize);
      this.buffer.consume(4 + frameSize);

      if (!this.state.foundIdentifier && type !== ChunkType.IDENTIFIER) {
        throw "malformed input: must begin with an identifier";
      }

      if (type === ChunkType.IDENTIFIER) {
        if (!Buffer.prototype.equals.call(data, IDENTIFIER)) {
          throw "malformed input: bad identifier";
        }
        this.state.foundIdentifier = true;
        continue;
      }

      if (type === ChunkType.COMPRESSED) {
        result.append(uncompress(data.subarray(4)));
      }
      if (type === ChunkType.UNCOMPRESSED) {
1)        result.append(data.subarray(4));
      }
    }
    if (result.length === 0) {
      return null;
    }
    return result;
  }
```

As you can see, checksum is not verified, bytes are appended to 'result'

### Proof of Concept

How to reproduce:

get poc via [gist link](https://gist.github.com/gln7/aab55674431b1c8d42a59ccf9d7cbf60) and run it:

```
$ node dec1.mjs 
checking chunk type=255
checking chunk type=1
got uncompressed chunk..
Decompressed ok 124 bytes
```

## Which versions are affected by GHSA-m9c9-mc2h-9wjw?

2 open source packages ship an affected version, including @lodestar/reqresp.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `@lodestar/reqresp` | npm | All versions | 1.25.0 |
| `@lodestar/reqresp` | npm | All versions | 1.25.0 |

## How do I fix GHSA-m9c9-mc2h-9wjw?

Upgrade @lodestar/reqresp to 1.25.0 or later.

## Is GHSA-m9c9-mc2h-9wjw being exploited?

There is no known exploitation of GHSA-m9c9-mc2h-9wjw in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for GHSA-m9c9-mc2h-9wjw and fix it if it is affected.

What it is: GHSA-m9c9-mc2h-9wjw is a vulnerability in @lodestar/reqresp, published on 14 Jan 2025. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of GHSA-m9c9-mc2h-9wjw in the wild and no public exploit code.

Affected packages and fixed versions:
- @lodestar/reqresp (npm): affected all versions; fixed in 1.25.0
- @lodestar/reqresp (npm): affected all versions; fixed in 1.25.0

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/GHSA-m9c9-mc2h-9wjw/ (Markdown: https://insights.sbomify.com/GHSA-m9c9-mc2h-9wjw/index.md)
```

## Sources

- OSV: https://osv.dev/vulnerability/GHSA-m9c9-mc2h-9wjw

---
From sbomify Insights: https://insights.sbomify.com/GHSA-m9c9-mc2h-9wjw/
Summaries are generated and may contain mistakes; the official description above is the record.