# CVE-2021-43839: Drainage of FeeCollector's Block Transaction Fees

> Attackers can drain block transaction fees from the FeeCollector by sending crafted Ethereum transactions, affecting Cronos blockchain validator nodes.

- **Severity:** High 7.5 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 21 Dec 2021
- **Updated:** 4 Aug 2024
- **Also known as:** GHSA-f854-hpxv-cw9r

## What is CVE-2021-43839?

CVE-2021-43839 is a high-severity vulnerability in crypto-org-chain cronos, published on 21 Dec 2021. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

Cronos is a commercial implementation of a blockchain. In Cronos nodes running versions before v0.6.5, it is possible to take transaction fees from Cosmos SDK's FeeCollector for the current block by sending a custom crafted MsgEthereumTx. This problem has been patched in Cronos v0.6.5. There are no tested workarounds. All validator node operators are recommended to upgrade to Cronos v0.6.5 at their earliest possible convenience.

Weakness: CWE-670 (Always-Incorrect Control Flow Implementation)

## Which versions are affected by CVE-2021-43839?

8 open source packages ship an affected version, including github.com/crypto-org-chain/cronos, github.com/tharsis/ethermint and github.com/tharsis/evmos. It affects 3 products.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `github.com/crypto-org-chain/cronos` | Go | All versions | 0.6.5 |
| `github.com/crypto-org-chain/cronos` | Go | All versions | 0.6.5 |
| `github.com/tharsis/ethermint` | Go | All versions | 0.7.3 |
| `github.com/tharsis/ethermint` | Go | All versions | 0.7.3 |
| `github.com/tharsis/ethermint` | Go | From 0.8.0 | 0.10.0 |
| `github.com/tharsis/ethermint` | Go | From 0.8.0 | 0.10.0 |
| `github.com/tharsis/evmos` | Go | All versions to 0.4.2 | None |
| `github.com/tharsis/evmos` | Go | All versions to 0.4.2 | None |

Products: Crypto Cronos, Crypto Ethermint, Crypto Evmos.

## How do I fix CVE-2021-43839?

Upgrade github.com/crypto-org-chain/cronos to 0.6.5 or later.

## Is CVE-2021-43839 being exploited?

There is no known exploitation of CVE-2021-43839 in the wild and no public exploit code.

## Other vulnerabilities in crypto-org-chain cronos

- [CVE-2022-35936](https://insights.sbomify.com/CVE-2022-35936/): Ethermint DoS through Unintended Contract Selfdestruct (high 8.2)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-43839 and fix it if it is affected.

What it is: CVE-2021-43839 is a high-severity vulnerability in crypto-org-chain cronos, published on 21 Dec 2021. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2021-43839 in the wild and no public exploit code.

Affected packages and fixed versions:
- github.com/crypto-org-chain/cronos (Go): affected all versions; fixed in 0.6.5
- github.com/crypto-org-chain/cronos (Go): affected all versions; fixed in 0.6.5
- github.com/tharsis/ethermint (Go): affected all versions; fixed in 0.7.3
- github.com/tharsis/ethermint (Go): affected all versions; fixed in 0.7.3
- github.com/tharsis/ethermint (Go): affected from 0.8.0; fixed in 0.10.0
- github.com/tharsis/ethermint (Go): affected from 0.8.0; fixed in 0.10.0
- github.com/tharsis/evmos (Go): affected all versions up to 0.4.2; no fix listed
- github.com/tharsis/evmos (Go): affected all versions up to 0.4.2; no fix listed

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/CVE-2021-43839/ (Markdown: https://insights.sbomify.com/CVE-2021-43839/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-43839
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-43839
- OSV: https://osv.dev/vulnerability/CVE-2021-43839

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-43839/
Summaries are generated and may contain mistakes; the official description above is the record.