VulnerabilityPublished 13 Aug 2026Updated 29 Oct 2026

CVE-2025-59420: Authlib · JWS/JWT accepts unknown crit headers (RFC violation → possible authz bypass)

Affects weaviate-cliSource GCVE Database

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Not known to be exploited · CVSS 7.5 High : upgrade to 3.2.4 soon.

Data as of 30 Oct 2026, 07:30 UTC

CVSS 3.1 base score

7.5High

How severe the flaw is on the 0–10 CVSS scale.

Patch: Available – fixed in 3.2.4

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N

Attack Vector: Network
Attack Complexity: Low
Privileges Required: None
User Interaction: None
Scope: Unchanged
Confidentiality: None
Integrity: High
Availability: None

Bold values are the worst case: easiest to exploit or largest impact.

Attack Vector: Network: The vulnerable component is bound to the network stack and the set of possible attackers extends beyond the other options listed, up to and including the entire Internet. Such a vulnerability is often termed 'remotely exploitable' and can be thought of as an attack being exploitable at the protocol level one or more network hops away (e.g., across one or more routers).
Attack Complexity: Low: Specialized access conditions or extenuating circumstances do not exist. An attacker can expect repeatable success against the vulnerable component.
Privileges Required: None: The attacker is unauthorized prior to attack, and therefore does not require any access to settings or files to carry out an attack.
User Interaction: None: The vulnerable system can be exploited without any interaction from any user.
Scope: Unchanged: An exploited vulnerability can only affect resources managed by the same security authority. In this case, the vulnerable component and the impacted component are either the same, or both are managed by the same security authority.
Confidentiality: None: There is no loss of confidentiality within the impacted component.
Integrity: High: There is a total loss of integrity, or a complete loss of protection. For example, the attacker is able to modify any/all files protected by the impacted component. Alternatively, only some files can be modified, but malicious modification would present a direct, serious consequence to the impacted component.
Availability: None: There is no impact to availability within the impacted component.

Definitions: FIRST CVSS v3.1 specification.

Exploitation evidence

Disclosed: evidence found.
CVE published 13 Aug 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponized: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 29 Oct 2026.

Disclosed: The CVE record is public on cve.org. Its publication is t = 0.
Detectable: A public nuclei template can find exposed instances, for defenders and attackers alike.
Weaponized: A Metasploit exploit module or Exploit-DB entry exists (Metasploit scanner modules do not count), or CISA SSVC or the CVSS exploit maturity reports a public proof of concept.
Exploited in the wild: CISA KEV lists it, CISA SSVC rates exploitation active, or a source reports attacks.
Observed by OffSeq Mirage: OffSeq Mirage honeypot sensors recorded attack traffic for this CVE, or found exposed hosts without attack traffic.

Moments are spaced evenly, not to scale; a dashed line marks a gap of six months or more. Deltas count from t = 0. Sources that give only a date (CISA KEV, Exploit-DB, or a time of exactly 00:00Z) read “same day” rather than hours. Metasploit modules carry the flaw’s disclosure date, not their release date, and nuclei templates carry no date, so both appear above but not on the timeline.

What to do

Upgrade weaviate-cli to 3.2.4.

Affected software

Product	Affected	Fixed in
Homebrewweaviate-cli`pkg:brew/weaviate-cli`Other threats	Affected >=3.0.2 <3.2.4	Fixed in 3.2.4

Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.

Description

## Summary Authlib’s JWS verification accepts tokens that declare unknown critical header parameters (`crit`), violating RFC 7515 “must‑understand” semantics. An attacker can craft a signed token with a critical header (for example, `bork` or `cnf`) that strict verifiers reject but Authlib accepts. In mixed‑language fleets, this enables split‑brain verification and can lead to policy bypass, replay, or privilege escalation. ## Affected Component and Versions - Library: Authlib (JWS verification) - API: `authlib.jose.JsonWebSignature.deserialize_compact(...)` - Version tested: 1.6.3 - Configuration: Default; no allowlist or special handling for `crit` ## Details RFC 7515 (JWS) §4.1.11 defines `crit` as a “must‑understand” list: recipients MUST understand and enforce every header parameter listed in `crit`, otherwise they MUST reject the token. Security‑sensitive semantics such as token binding (e.g., `cnf` from RFC 7800) are often conveyed via `crit`. Observed behavior with Authlib 1.6.3: - When a compact JWS contains a protected header with `crit: ["cnf"]` and a `cnf` object, or `crit: ["bork"]` with an unknown parameter, Authlib verifies the signature and returns the payload without rejecting the token or enforcing semantics of the critical parameter. - By contrast, Java Nimbus JOSE+JWT (9.37.x) and Node `jose` v5 both reject such tokens by default when `crit` lists unknown names. Impact in heterogeneous fleets: - A strict ingress/gateway (Nimbus/Node) rejects a token, but a lenient Python microservice (Authlib) accepts the same token. This split‑brain acceptance bypasses intended security policies and can enable replay or privilege escalation if `crit` carries binding or policy information. ## Proof of Concept (PoC) This repository provides a multi‑runtime PoC demonstrating the issue across Python (Authlib), Node (`jose` v5), and Java (Nimbus). ### Prerequisites - Python 3.8+ - Node.js 18+ - Java 11+ with Maven ### Setup Enter the directory **authlib-crit-bypass-poc** & run following commands. ```bash make setup make tokens ``` ### Tokens minted - `tokens/unknown_crit.jwt` with protected header: `{ "alg": "HS256", "crit": ["bork"], "bork": "x" }` - `tokens/cnf_header.jwt` with protected header: `{ "alg": "HS256", "crit": ["cnf"], "cnf": {"jkt": "thumb-42"} }` ### Reproduction Run the cross‑runtime demo: ```bash make demo ``` Expected output for each token (strict verifiers reject; Authlib accepts): For `tokens/unknown_crit.jwt`: ``` Strict(Nimbus): REJECTED (unknown critical header: bork) Strict(Node jose): REJECTED (unrecognized crit) Lenient(Authlib): ACCEPTED -> payload={'sub': '123', 'role': 'user'} ``` For `tokens/cnf_header.jwt`: ``` Strict(Nimbus): REJECTED (unknown critical header: cnf) Strict(Node jose): REJECTED (unrecognized crit) Lenient(Authlib): ACCEPTED -> payload={'sub': '123', 'role': 'user'} ``` Environment notes: - Authlib version used: `1.6.3` (from PyPI) - Node `jose` version: `^5` - Nimbus JOSE+JWT version: `9.37.x` - HS256 secret is 32 bytes to satisfy strict verifiers: `0123456789abcdef0123456789abcdef` ## Impact - Class: Violation of JWS `crit` “must‑understand” semantics; specification non‑compliance leading to authentication/authorization policy bypass. - Who is impacted: Any service that relies on `crit` to carry mandatory security semantics (e.g., token binding via `cnf`) or operates in a heterogeneous fleet with strict verifiers elsewhere. - Consequences: Split‑brain acceptance (gateway rejects while a backend accepts), replay, or privilege escalation if critical semantics are ignored. ## References - RFC 7515: JSON Web Signature (JWS), §4.1.11 `crit` - RFC 7800: Proof‑of‑Possession Key Semantics for JWTs (`cnf`)

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