# CVE-2026-65630: Timing side-channel in pure-Erlang X25519 scalar multiplication leaks the private key in jose


- **Severity:** Medium 5.9 (`CVSS:4.0/AV:L/AC:H/AT:P/PR:N/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N`)
- **Exploited in the wild:** Not known
- **Fix available:** Yes
- **Published:** 26 Oct 2026
- **Updated:** 26 Oct 2026
- **Also known as:** AZL-111158, DEBIAN-CVE-2026-65630, EEF-CVE-2026-65630, GHSA-xvr2-gggj-h2pp, UBUNTU-CVE-2026-65630

## What is CVE-2026-65630?

CVE-2026-65630 is a medium-severity vulnerability in potatosalad jose, published on 26 Oct 2026. 

### Official description

Observable Timing Discrepancy vulnerability in potatosalad jose allows recovery of a long-term X25519 private key through a timing side channel in the pure-Erlang Curve25519 fallback.

The pure-Erlang X25519 implementation performs scalar multiplication over the secret private key using a recursive Montgomery ladder (jose_jwa_x25519:curve25519/2) whose clauses branch on individual bits of the clamped private scalar, and whose per-step operations (jose_jwa_x25519:montgomery_add/3 and jose_jwa_x25519:montgomery_double/1) and field inversion are built from value-dependent Erlang bignum arithmetic (multiplication, remainder, and modular exponentiation). Although the ladder is operation-count balanced and fixed at 254 steps, the concrete integer values processed at each step, and therefore the running time, depend on the secret scalar. The execution time of the public entry points jose_jwa_x25519:scalarmult/2, jose_jwa_x25519:x25519/2, jose_jwa_x25519:x25519_base/1, and jose_jwa_x25519:sk_to_pk/1 is thus a function of the private key.

This path is reachable from the public API, most notably when a service decrypts attacker-supplied ECDH-ES (JWE) messages with a long-term X25519 key (for example through JOSE.JWK.box_decrypt_ecdh_es/2, which reaches jose_jwa_curve25519:x25519_shared_secret/2 and the ladder). An attacker who can submit ciphertexts and measure decryption timing can, in principle, recover the private key bit by bit, defeating the resistance X25519 was designed to provide. Recovery of the key compromises the confidentiality and authenticity of all data protected by it.

This issue affects jose: from 1.10.0 before 1.11.13.

Weakness: CWE-208 (Observable Timing Discrepancy)

## Which versions are affected by CVE-2026-65630?

1 open source package ship an affected version, including jose.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `jose` | Hex | From 1.10.0 | 1.11.13 |

## How do I fix CVE-2026-65630?

Upgrade jose to 1.11.13 or later.

## Is CVE-2026-65630 being exploited?

There is no known exploitation of CVE-2026-65630 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-65630 and fix it if it is affected.

What it is: CVE-2026-65630 is a medium-severity vulnerability in potatosalad jose, published on 26 Oct 2026. 
Exploitation: There is no known exploitation of CVE-2026-65630 in the wild and no public exploit code.

Affected packages and fixed versions:
- jose (Hex): affected from 1.10.0; fixed in 1.11.13

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-2026-65630/ (Markdown: https://insights.sbomify.com/CVE-2026-65630/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-65630
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-65630
- OSV: https://osv.dev/vulnerability/CVE-2026-65630

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-65630/
Summaries are generated and may contain mistakes; the official description above is the record.