# CVE-2021-21271: Denial of service in TenderMint Core > Attackers can cause network disconnections and denial of service by exploiting inconsistent evidence timestamps in Tendermint Core consensus. - **Severity:** Medium 6.5 (`CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H`) - **Exploited in the wild:** Not known - **Login needed:** Any signed-in user - **Attackable:** Over the internet - **Victim action needed:** Not needed - **Fix available:** Yes - **Published:** 26 Jan 2021 - **Updated:** 3 Aug 2024 - **Also known as:** GHSA-p658-8693-mhvg, GO-2022-1052 ## What is CVE-2021-21271? CVE-2021-21271 is a medium-severity denial of service vulnerability in tendermint, published on 26 Jan 2021. Any signed-in user can exploit it over the network, with no action from the victim. ### Official description Tendermint Core is an open source Byzantine Fault Tolerant (BFT) middleware that takes a state transition machine - written in any programming language - and securely replicates it on many machines. Tendermint Core v0.34.0 introduced a new way of handling evidence of misbehavior. As part of this, we added a new Timestamp field to Evidence structs. This timestamp would be calculated using the same algorithm that is used when a block is created and proposed. (This algorithm relies on the timestamp of the last commit from this specific block.) In Tendermint Core v0.34.0-v0.34.2, the consensus reactor is responsible for forming DuplicateVoteEvidence whenever double signs are observed. However, the current block is still “in flight” when it is being formed by the consensus reactor. It hasn’t been finalized through network consensus yet. This means that different nodes in the network may observe different “last commits” when assigning a timestamp to DuplicateVoteEvidence. In turn, different nodes could form DuplicateVoteEvidence objects at the same height but with different timestamps. One DuplicateVoteEvidence object (with one timestamp) will then eventually get finalized in the block, but this means that any DuplicateVoteEvidence with a different timestamp is considered invalid. Any node that formed invalid DuplicateVoteEvidence will continue to propose invalid evidence; its peers may see this, and choose to disconnect from this node. This bug means that double signs are DoS vectors in Tendermint Core v0.34.0-v0.34.2. Tendermint Core v0.34.3 is a security release which fixes this bug. As of v0.34.3, DuplicateVoteEvidence is no longer formed by the consensus reactor; rather, the consensus reactor passes the Votes themselves into the EvidencePool, which is now responsible for forming DuplicateVoteEvidence. The EvidencePool has timestamp info that should be consistent across the network, which means that DuplicateVoteEvidence formed in this reactor should have consistent timestamps. This release changes the API between the consensus and evidence reactors. Weakness: CWE-400 (Uncontrolled Resource Consumption) ## Which versions are affected by CVE-2021-21271? 3 open source packages ship an affected version, including github.com/tendermint/tendermint. It affects 1 product. | Package | Ecosystem | Affected | Fixed in | | --- | --- | --- | --- | | `github.com/tendermint/tendermint` | Go | From 0.34.0 | 0.34.3 | | `github.com/tendermint/tendermint` | Go | From 0.34.0 | 0.34.3 | | `github.com/tendermint/tendermint` | Go | From 0.34.0 | 0.34.3 | Products: Tendermint Tendermint. ## How do I fix CVE-2021-21271? Upgrade github.com/tendermint/tendermint to 0.34.3 or later. ## Is CVE-2021-21271 being exploited? There is no known exploitation of CVE-2021-21271 in the wild and no public exploit code. ## Other vulnerabilities in tendermint - [CVE-2019-25072](https://insights.sbomify.com/CVE-2019-25072/): Uncontrolled resource consumption in github.com/tendermint/tendermint (high 7.5) - [CVE-2020-15091](https://insights.sbomify.com/CVE-2020-15091/): Denial of Service in TenderMint (medium 6.5) - [CVE-2020-5303](https://insights.sbomify.com/CVE-2020-5303/): Denial of service in Tendermint (low 3.1) ## Fix prompt for AI coding agents ```text Check this codebase for CVE-2021-21271 and fix it if it is affected. What it is: CVE-2021-21271 is a medium-severity denial of service vulnerability in tendermint, published on 26 Jan 2021. Any signed-in user can exploit it over the network, with no action from the victim. Exploitation: There is no known exploitation of CVE-2021-21271 in the wild and no public exploit code. Affected packages and fixed versions: - github.com/tendermint/tendermint (Go): affected from 0.34.0; fixed in 0.34.3 - github.com/tendermint/tendermint (Go): affected from 0.34.0; fixed in 0.34.3 - github.com/tendermint/tendermint (Go): affected from 0.34.0; fixed in 0.34.3 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-2021-21271/ (Markdown: https://insights.sbomify.com/CVE-2021-21271/index.md) ``` ## Sources - CVE record: https://www.cve.org/CVERecord?id=CVE-2021-21271 - NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-21271 - OSV: https://osv.dev/vulnerability/CVE-2021-21271 --- From sbomify Insights: https://insights.sbomify.com/CVE-2021-21271/ Summaries are generated and may contain mistakes; the official description above is the record.