CVE-2026-101917VulnerabilityPublished 30 Sep 2026Updated 27 Oct 2026

hermes-agent · PyJWT: PyJWKClient still amplifies unauthenticated JWKS fetches on unknown kid values (incomplete fix of

Affects hermes-agentSource GCVE Database

Authoritative record:CVE-2026-101917· Medium 5.3

Not known to be exploited · CVSS 5.3 Medium : upgrade to 0.22.4 when convenient.

Data as of 27 Oct 2026, 21:01 UTC

CVSS 3.1 base score

5.3Medium

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

Patch: Available – fixed in 0.22.4

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

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

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: None: There is no loss of integrity within the impacted component.
Availability: Low: Performance is reduced or there are interruptions in resource availability. Even if repeated exploitation of the vulnerability is possible, the attacker does not have the ability to completely deny service to legitimate users. The resources in the impacted component are either partially available all of the time, or fully available only some of the time, but overall there is no direct, serious consequence to 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

Upgrade to PyJWT version 2.14.0 or later, which includes a fix that enforces a 30-second cooldown between forced JWKS refreshes for unknown 'kid' values, preventing unbounded fetches. Until upgrading, consider disabling JWKS caching or implementing external rate limiting on JWKS endpoint requests if feasible. The fix is official and included in the released version 2.14.0.

Description

PyJWT versions up to 2.13.0 have a denial-of-service vulnerability where unauthenticated requests with unknown 'kid' values cause repeated JWKS endpoint fetches without rate limiting or caching of negative results. This leads to excessive outbound HTTP requests and JSON parsing on the victim server, potentially exhausting resources and causing authentication outages. The issue was fixed in PyJWT 2.14.0 by adding a cooldown period to limit forced JWKS refreshes on unknown kids.

Impact

An unauthenticated attacker can cause the victim server to repeatedly fetch and parse JWKS data by sending tokens with unknown 'kid' values. This results in amplified outbound HTTP requests and CPU usage on the victim, potentially exhausting server resources and causing authentication failures or outages. The vulnerability does not allow data disclosure or code execution but can cause denial of service due to resource exhaustion.

Summary

CVE-2026-101917 describes a denial-of-service vulnerability in PyJWT's PyJWKClient component affecting versions up to 2.13.0. When a JWT token contains an unknown 'kid' (key ID) in its header, PyJWKClient forcibly refreshes the JWKS (JSON Web Key Set) cache by fetching the JWKS endpoint anew on every request, without rate limiting or negative caching. This behavior allows an attacker to cause the victim server to repeatedly fetch and parse JWKS data, amplifying resource consumption and potentially causing service disruption. The flaw was incompletely fixed in version 2.13.0, but a complete fix was implemented in version 2.14.0, which introduced a 30-second cooldown to prevent unbounded JWKS refreshes for unknown kids.

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Exploitation evidence

What to do

Affected software

Description

AI analysisMachine-generated, updated 27 Oct 2026, 21:01 UTC

Technical details

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