CVE-2026-102268VulnerabilityPublished 30 Sep 2026Updated 27 Oct 2026

hermes-agent · PyJWT: Asymmetric-PEM detection bypass: whitespace/line-ending-mutated public keys skip the HS/asymmetric confusion

Affects hermes-agentSource GCVE Database

Authoritative record:CVE-2026-102268· Critical 9.1

Not known to be exploited · CVSS 9.1 Critical : upgrade to 0.22.4 as a priority.

Data as of 27 Oct 2026, 21:00 UTC

CVSS 3.1 base score

9.1Critical

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:H/I:H/A:N

Attack Vector: Network
Attack Complexity: Low
Privileges Required: None
User Interaction: None
Scope: Unchanged
Confidentiality: High
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: High: There is total loss of confidentiality, resulting in all resources within the impacted component being divulged to the attacker. Alternatively, access to only some restricted information is obtained, but the disclosed information presents a direct, serious impact.
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 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 PyJWT to version 0.22.4 or later, where the asymmetric key detection has been corrected to handle these PEM variants properly. Avoid mixing HMAC and asymmetric algorithms in the allowed algorithms list for JWT verification. If upgrading is not immediately possible, ensure that PEM keys are normalized to a format recognized by PyJWT's is_pem_format() function to prevent bypass.

Description

PyJWT versions before 0.22.4 contain a vulnerability where malformed PEM public keys with whitespace or unusual line endings bypass the asymmetric key detection. This causes the public key to be used as an HMAC secret, allowing an attacker who knows the public key to forge valid HS256 tokens when the verification algorithm list mixes HMAC and asymmetric algorithms.

Impact

An attacker who knows the public verification key can forge valid HS256 JWT tokens, effectively allowing universal token forgery and privilege escalation (e.g., forging tokens with superadmin privileges). This occurs only if the application uses a mixed algorithm allow-list including both asymmetric and HMAC algorithms and passes the public key in a PEM format variant that bypasses PyJWT's PEM detection. The vulnerability has a critical impact on confidentiality and integrity of JWT authentication.

Summary

The vulnerability arises because PyJWT's is_pem_format() function uses a strict regex that fails to recognize PEM public keys with marker-adjacent whitespace, CR-only line terminators, or folded single-line formatting, while the cryptography library's loader accepts these keys. As a result, the asymmetric-key rejection guard in HMACAlgorithm.prepare_key() is bypassed, causing the public key to be used as an HMAC secret. This enables an attacker with knowledge of the public key to forge valid HS256 tokens if the allowed algorithms include both an asymmetric algorithm (e.g., ES256 or RS256) and HS256. The issue was confirmed on PyJWT 2.13.0 with cryptography 49.0.0 and fixed in PyJWT version 0.22.4.

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Exploitation evidence

What to do

Affected software

Description

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

Technical details

References

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