CVE-2023-34451

CometBFT may duplicate transactions in the mempool's data structures

Workarounds

• Increasing the value of cache_size in config.toml makes it very difficult to effectively attack a full node.
• Not exposing the transaction submission RPC's would mitigate the probability of a successful attack, as the attacker would then have to create a modified (byzantine) full node to be able to perform the attack via p2p.

References

• PR that introduced the map to track transactions in the mempool.
• PR containing the fix.

The mempool maintains two data structures to keep track of outstanding transactions: a list and a map.
These two data structures are supposed to be in sync all the time in the sense that the map tracks the index (if any) of the transaction in the list.

Unfortunately, it is possible to have them out of sync. When this happens, the list may contain several copies of the same transaction.
Because the map tracks a single index, it is then no longer possible to remove all the copies of the transaction from the list.
This happens even if the duplicated transaction is later committed in a block.
The only way to remove the transaction is by restarting the node.

These are the steps to cause the above duplication problem. Everything should happen within one height, that is no FinalizeBlock or BeginBlock ABCI calls should happen while these steps are reproduced:

1. send transaction tx1 to the target full node via RPC
2. send N more different transactions to the target full node, where N should be higher than the node's configured value for cache_size in config.toml
3. send transaction tx1 again to the target full node

One of the copies of tx1 is now stuck in the mempool's data structures. Effectively causing a memory leak, and having that node gossiping that transaction to its peers forever.

The above problem can be repeated on and on until a sizable number of transactions are stuck in the mempool, in order to try to bring down the target node.

This problem is present in releases: v0.37.0, and v0.37.1, as well as in v0.34.28, and all previous releases of the CometBFT repo. It will be fixed in releases v0.34.29 and v0.37.2.

CVE-2023-34451 has a CVSS score of 8.2 (High). The vector is network-reachable, no privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (0.34.29, 0.37.2); upgrading removes the vulnerable code path.

Kodem intelligence

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The PR containing the fix is here.

1. What is CVE-2023-34451? CVE-2023-34451 is a high-severity security vulnerability in github.com/cometbft/cometbft (go), affecting versions < 0.34.29. It is fixed in 0.34.29, 0.37.2.
2. How severe is CVE-2023-34451? CVE-2023-34451 has a CVSS score of 8.2 (High). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
3. Which versions of github.com/cometbft/cometbft are affected by CVE-2023-34451? github.com/cometbft/cometbft (go) versions < 0.34.29 is affected.
4. Is there a fix for CVE-2023-34451? Yes. CVE-2023-34451 is fixed in 0.34.29, 0.37.2. Upgrade to this version or later.
5. Is CVE-2023-34451 exploitable, and should I be worried? Whether CVE-2023-34451 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
6. What actually determines whether CVE-2023-34451 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
7. How do I fix CVE-2023-34451?
   • Upgrade github.com/cometbft/cometbft to 0.34.29 or later
   • Upgrade github.com/cometbft/cometbft to 0.37.2 or later

Other vulnerabilities in github.com/cometbft/cometbft