VulnerabilityPublished 13 Aug 2026Updated 29 Oct 2026

CVE-2026-48523: PyJWT · Algorithm allow-list bypass when decoding with `PyJWK` / `PyJWKClient` keys

Affects hermes-agentSource GCVE Database

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Authoritative record:CVE-2026-48523· Medium 5.4

Not known to be exploited · CVSS 5.4 Medium : upgrade to 2026.7.1 when convenient.

Data as of 30 Oct 2026, 09:02 UTC

CVSS 3.1 base score

5.4Medium

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

Patch: Available – fixed in 2026.7.1

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

Attack Vector: Network
Attack Complexity: Low
Privileges Required: Low
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: Low: Specialized access conditions or extenuating circumstances do not exist. An attacker can expect repeatable success against the vulnerable component.
Privileges Required: Low: The attacker is authorized with (i.e., requires) privileges that provide basic user capabilities that could normally affect only settings and files owned by a user. Alternatively, an attacker with Low privileges may have the ability to cause an impact only to non-sensitive resources.
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 May 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 hermes-agent to 2026.7.1.

Affected software

Product	Affected	Fixed in
Homebrewhermes-agent`pkg:brew/hermes-agent`Other threats	Affected >=2026.4.30 <2026.7.1	Fixed in 2026.7.1

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

AI-suggested

A patch is available in version 2026.7.1 that fixes this vulnerability. Users should upgrade to this version or later to remediate the issue. No additional mitigations are required if the patch is applied. Until patched, deployments should be aware that algorithm allow-list enforcement can be bypassed when using PyJWK or PyJWKClient keys.

Description

PyJWT versions 2.9.0 through 2.12.1 contain a vulnerability allowing an algorithm allow-list bypass when decoding JWTs with PyJWK or PyJWKClient keys. The library checks the JWT header algorithm against an allowed list but verifies the signature using the algorithm bound to the PyJWK object instead of the header algorithm. This allows an attacker controlling a registered JWK private key to sign tokens with disallowed algorithms while advertising allowed ones, bypassing algorithm restrictions. The issue affects the documented PyJWKClient usage flow and requires control of a registered key. A fix is available in version 2026.7.1.

Impact

An attacker with control over a registered JWK private key can bypass the verifier's algorithm allow-list policy by signing JWTs with disallowed algorithms while advertising allowed algorithms in the JWT header. This undermines the intended cryptographic policy enforcement, potentially allowing weaker or unintended algorithms to be accepted. The confidentiality impact depends on deployment context; if algorithm policy is used as an authentication or authorization boundary, this can lead to unauthorized access or privilege escalation. The vulnerability does not allow forgery without a valid key but compromises algorithm enforcement in affected environments.

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Affected software

Description

AI analysisMachine-generated, updated 30 Oct 2026, 09:02 UTC

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