VulnerabilityPublished 30 Sep 2026Updated 27 Oct 2026

CVE-2026-102269: PyJWT · Non-canonical signature segments enable raw-token revocation bypass

Affects hermes-agentSource GCVE Database

Authoritative record:CVE-2026-102269· Medium 4.8

Not known to be exploited · CVSS 4.8 Medium : upgrade to 0.22.4 when convenient.

Data as of 27 Oct 2026, 21:00 UTC

CVSS 3.1 base score

4.8Medium

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

Patch: Available – fixed in 0.22.4

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

Attack Vector: Network
Attack Complexity: High
Privileges Required: None
User Interaction: None
Scope: Unchanged
Confidentiality: Low
Integrity: Low
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: High: A successful attack depends on conditions beyond the attacker's control. That is, a successful attack cannot be accomplished at will, but requires the attacker to invest in some measurable amount of effort in preparation or execution against the vulnerable component before a successful attack can be expected. For example, a successful attack may require an attacker to: gather knowledge about the environment in which the vulnerable target/component exists; prepare the target environment to improve exploit reliability; or inject themselves into the logical network path between the target and the resource requested by the victim in order to read and/or modify network communications (e.g., a man in the middle attack).
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: Low: There is some loss of confidentiality. Access to some restricted information is obtained, but the attacker does not have control over what information is obtained, or the amount or kind of loss is limited. The information disclosure does not cause a direct, serious loss to the impacted component.
Integrity: Low: Modification of data is possible, but the attacker does not have control over the consequence of a modification, or the amount of modification is limited. The data modification does not have a direct, serious impact on 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 28 Sep 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponised: 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 26 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.
Weaponised: Public exploit code exists in Metasploit or Exploit-DB, 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 hermes-agent to 0.22.4.

Affected software

Product	Affected	Fixed in
Homebrewhermes-agent`pkg:brew/hermes-agent`Other threats	Affected >=0.21.6 <0.22.4 >=2026.4.30 <=2026.9.24	Fixed in 0.22.4

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

AI-suggested

A fix is available in PyJWT version 0.22.4 and later, which rejects signature segments containing non-canonical Base64URL characters and padding before verification. Until the fixed version is released and adopted, applications should avoid using the raw serialized token string as the identity for revocation or logout. Instead, they should use a semantic identifier such as the 'jti' claim to track token state. The vendor has confirmed the fix and it is ready for release but not yet published.

Description

PyJWT versions including 2.13.0 accept compact JWS signature segments with non-canonical Base64URL characters, allowing alternate token serializations that decode to the same signature bytes and claims. This can enable bypass of raw-token-based revocation or logout mechanisms if the application uses the raw serialized token string as the identity for revocation or replay state. The vulnerability does not allow signature forgery or claim alteration. A fix has been developed to reject non-canonical Base64URL characters in signature segments but is not yet released.

Impact

The impact is limited to applications that use the raw serialized JWT token string as the identity for logout, revocation, replay, rate-limiting, or cache state. Under this condition, an attacker with a valid token can bypass logout or token-specific revocation by presenting an alternate serialization of the same token that passes verification but has a different raw string hash. The vulnerability does not allow forging signatures or modifying claims. The CVSS 3.1 score is 4.8 (medium severity) reflecting limited impact and the requirement for specific unsafe application behavior.

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Affected software

Description

AI analysisMachine-generated, updated 27 Oct 2026, 21:00 UTC

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