CVE-2026-45363 | `jwt` (Ruby gem) - empty-key HMAC bypass

ruby-jwt is a Ruby implementation of the RFC 7519 OAuth JSON Web Token standard. Prior to 2.10.3 and 3.2.0, JWT.decode(token, '', true, algorithm: 'HS256') accepts an attacker-forged token because OpenSSL::HMAC.digest('SHA256', '', payload) returns a valid digest under an empty key and no empty-key precondition exists in the HMAC algorithm. The same path is reached when a keyfinder block or key_finder: argument returns an empty string, nil, or an array containing nil for an unknown key, affecting HS256, HS384, and HS512 verification through JWT.decode and JWT::EncodedToken#verify_signature!. This issue is fixed in versions 2.10.3 and 3.2.0.

Published: 2026-07-14 Last update: 2026-07-15 Assigner: [email protected] Source: [email protected]
NVD Status：Deferred，CVE State: published
View at NVD, CVE.org, EUVD

CVE-2026-45363 is rated Moderate Risk (42/100): CVSS Critical severity, with low exploitation likelihood (EPSS 0.24%). Review affected assets and schedule remediation.

Risk is dynamic; we continuously reassess and refresh what is shown on this page as upstream context changes.

Exploit prediction scoring system (EPSS) score for CVE-2026-45363

EPSS lead: Daily EPSS estimates relative likelihood of exploitation; percentile ranks this CVE among scored vulnerabilities (higher = more severe relative rank).

# Date Old EPSS score New EPSS score Delta (New - Old)
1 2026-07-15 0.02% 0.24% +0.22%
2 2026-06-12 — 0.02% —

Full EPSS history (2 records total)

Common vulnerability scoring system (CVSS) metrics for CVE-2026-45363

CVSS metrics for this CVE.

Base score Version Severity Vector Exploitability Impact Score source
9.1 3.1 CRITICAL
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N Click to expand
Attack vector (AV:N)
Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
Attack complexity (AC:L)
Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
Privileges required (PR:N)
No account or special rights needed—anonymous or random user is enough.
User interaction (UI:N)
Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:U)
Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:H)
Serious risk that confidential data gets exposed in a big way.
Integrity (I:H)
They could widely tamper with or forge data—trust in the data is badly hurt.
Availability (A:N)
Service keeps running; no real outage angle.
 3.9 5.2 [email protected]

Weakness enumeration for CVE-2026-45363

GitHub Security Advisory for CVE-2026-45363

GHSA-c32j-vqhx-rx3x · Severity: high · Ecosystem: rubygems — ruby-jwt: Empty-key HMAC bypass; cross-language sibling of CVE-2026-44351

OS Trackers for CVE-2026-45363

vendor priority summary link
debian not yet assigned CVE-2026-45363 not yet assigned priority: Debian including 1 source packages (ruby-jwt), 5 status rows across 5 suites (bookworm, bullseye, forky, sid, trixie): open 3, resolved 2. https://security-tracker.debian.org/tracker/CVE-2026-45363
redhat high — https://access.redhat.com/security/cve/CVE-2026-45363
suse high — https://www.suse.com/security/cve/CVE-2026-45363/
ubuntu medium CVE-2026-45363 medium priority: Ubuntu including 1 source packages (ruby-jwt), 6 status rows across 6 suites (bionic, focal, jammy, noble, resolute, upstream): needs-triage 6. https://ubuntu.com/security/CVE-2026-45363

Affected software / configurations for CVE-2026-45363

Vendor Product Version Raw CPE
No affected products in dataset.

References for CVE-2026-45363

cvelogic Threat Intelligence