# Ed25519 Signature Malleability in ed25519-java Due to Missing Scalar Range Check

Advisory record · `GHSA-p53j-g8pw-4w5f`

- **Identifiers:** `GHSA-p53j-g8pw-4w5f` · `CVE-2020-36843`
- **State:** Confirmed
- **Severity:** CVSS 4.3 Medium
- **Critical:** No
- **Weakness (CWE):** [CWE-347](https://cwe.mitre.org/data/definitions/347.html)
- **Tags:** [Weak cryptography or TLS](https://agentprime.io/advisories/tag/weak-crypto.md)
- **Published:** 13 Mar 2025
- **Updated:** 10 Sept 2026
- **Reviewed by a person:** No

Published by the GitHub Advisory Database at 13 Mar 2025, 06:30 UTC. agentprime has not analysed this yet, so whether it affects any app is not known.

## Affected packages

- `net.i2p.crypto:eddsa` (Maven): affected `<=0.3.0`; no fixed version yet
- `net.i2p:i2p` (Maven): affected `<0.9.39`; fixed in `0.9.39`

## Machine-written summary

Summary written by Claude Haiku from the source advisory. Not reviewed by a person.

> net.i2p.crypto:eddsa through version 0.3.0 accepts malleable Ed25519 signatures and does not meet the SUF-CMA property. An attacker can create new valid signatures for a known message that differ from the original. No fixed version of net.i2p.crypto:eddsa is listed; net.i2p:i2p versions before 0.9.39 are also affected, so upgrade it to 0.9.39.

Written 2 Nov 2026.

## Not analysed yet

We haven’t published our analysis of this Advisory yet. Once a person has reviewed it, this page will say what’s vulnerable, what has to be true for your app to be affected, and how to check.

## Severity and exploitation

- 4.3 Medium, CVSS 3.1: `CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:C/C:N/I:L/A:N`, from CNA (mitre)

- **CISA KEV:** Not listed.
- **EPSS:** 0.0014, the 3rd percentile, on 14 Nov 2026: FIRST’s estimate of the chance of exploitation in the next 30 days.

## Timeline

- 31 Oct 2026, 14:18 UTC: First seen by agentprime
- 31 Oct 2026, 14:18 UTC: [Confirmed by OSV](https://osv.dev/vulnerability/GHSA-p53j-g8pw-4w5f)

## Sources

- [GitHub Advisory Database: GHSA-p53j-g8pw-4w5f](https://github.com/advisories/GHSA-p53j-g8pw-4w5f)
- [OSV: GHSA-p53j-g8pw-4w5f](https://osv.dev/vulnerability/GHSA-p53j-g8pw-4w5f)
- <https://nvd.nist.gov/vuln/detail/CVE-2020-36843>
- <https://github.com/str4d/ed25519-java/issues/82#issue-727629226>
- <https://github.com/i2p/i2p.i2p/commit/d7d1dcb5399c61cf2916ccc45aa25b0209c88712#diff-658f7b1aa34b58d27796fccdb8b756c72702d64ae44703374960f1cb89a5a5c3>
- <https://eprint.iacr.org/2020/1244>
- <https://github.com/str4d/ed25519-java>

Facts on this page come from the GitHub Advisory Database (CC-BY 4.0), OSV and the other sources listed, as published. We don’t reproduce full advisory descriptions, which can contain exploit code.

## Check whether this affects you

A Match means an installed version is in the affected range above. Most don’t affect the app; agentprime hasn’t analysed this one yet.

- With the agentprime MCP server (<https://api.agentprime.io/mcp>), ask your agent to check the project: `check_lockfile` sends a lockfile, `check_packages` a list of installed packages, and both return the Matches and the upgrades that clear them. `get_advisory` returns this record. Setup: <https://agentprime.io/mcp.md>
- In a browser: <https://agentprime.io/check/> reads your lockfile in the browser, never uploading it.
- Whether it touches your code, with file and line: the Claude Code plugin, <https://agentprime.io/plugin.md>
- As JSON: <https://api.agentprime.io/v1/advisories/GHSA-p53j-g8pw-4w5f>, or `POST https://api.agentprime.io/v1/match` with your packages (<https://agentprime.io/api.md>)

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The web page: <https://agentprime.io/advisories/GHSA-p53j-g8pw-4w5f/>. Everything for agents: <https://agentprime.io/llms.txt>.