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

Status: published. Published: 2026-10-26. Updated: 2026-11-03.

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.

## Remediation

- fix: The reporting source identifies this reference as a patch. Check the advisory for affected versions and supported release branches. (source: CNA: EEF) — https://github.com/potatosalad/erlang-jose/commit/bfd336c0062bff93e65d08c22361897e96afd956

## Affected products and versions

- potatosalad / jose (jose): ≥ 1.7.7; < 1.11.13 (affected, semver). Source: CNA: EEF
- potatosalad / jose (potatosalad/erlang-jose): ≥ d19e1ba68d88c68d29aa942be2573a22dbafca1f; < bfd336c0062bff93e65d08c22361897e96afd956 (affected, git). Source: CNA: EEF

## Severity and prioritization

- CVSS 4.0: 6.9 (medium); 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; source: CNA: EEF

- CISA KEV: No listing in collected sources

- EPSS: 0.24% as of 2026-11-03; percentile 14.46%

- SSVC: exploitation poc; automatable no; technical impact partial; source ADP: CISA-ADP

- Weaknesses: CWE-407

## Exploit evidence

No exploit evidence in collected sources. This is not proof of no exploitation.

## References

- https://github.com/potatosalad/erlang-jose/security/advisories/GHSA-3m45-vrpj-xmrq (CNA: EEF; vendor-advisory, related)

- https://cna.erlef.org/cves/CVE-2026-65631.html (CNA: EEF; related)

- https://osv.dev/vulnerability/EEF-CVE-2026-65631 (CNA: EEF; related)

- https://github.com/potatosalad/erlang-jose/commit/d19e1ba68d88c68d29aa942be2573a22dbafca1f (CNA: EEF; related)

- https://github.com/potatosalad/erlang-jose/commit/bfd336c0062bff93e65d08c22361897e96afd956 (CNA: EEF; patch)

## Provenance

- CNA: EEF: https://www.cve.org/CVERecord?id=CVE-2026-65631; retrieved 2026-11-03; source updated 2026-11-03

- FIRST EPSS: https://api.first.org/data/v1/epss?cve=CVE-2026-65631; retrieved 2026-11-03; source updated Not reported

Revision: 629f067f27b9fba0545519dd0e51c525e60e536e0346cce140509bf5e619a552

Canonical: https://y2.dev/cve/CVE-2026-65631

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