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CVE-2026-48526VulnerabilityPublished Updated

hermes-agent · PyJWT: Public-key JWK accepted as HMAC secret enables forged HS256 tokens when mixed families are allowed

Affects hermes-agentSource GCVE Database

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Authoritative record:CVE-2026-48526· High 7.4

Not known to be exploited · CVSS 7.4 High : upgrade to 2026.7.1 soon.

Data as of 30 Oct 2026, 09:00 UTC

CVSS 3.1 base score
7.4High
How severe the flaw is on the 0–10 CVSS scale.
Patch
Available – fixed in 2026.7.1
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N

Exploitation evidence

  1. Disclosed: evidence found.

    CVE published 28 May 2026

  2. Detectable: no evidence on record.

    No public nuclei template indexed

  3. Weaponized: no evidence on record.

    No public exploit code indexed in Metasploit or Exploit-DB

  4. Exploited in the wild: no evidence on record.

    Not in CISA KEV and no source reports exploitation

  5. Observed by OffSeq 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.

What to do

Upgrade hermes-agent to 2026.7.1.

Affected software

ProductAffectedFixed in
Homebrewhermes-agentpkg:brew/hermes-agentOther threatsAffected
  • >=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 PyJWT version 2026.7.1 that addresses this vulnerability. Users should upgrade to this fixed version to prevent exploitation. The vulnerability requires a misconfiguration where both symmetric and asymmetric algorithms are allowed simultaneously and a public JWK is used as the key; correcting such verifier configurations also mitigates the risk. No additional mitigations are necessary once the patch is applied.

Description

PyJWT versions from 2026.4.30 up to but not including 2026.7.1 contain a vulnerability where a verifier configured to accept both symmetric (HMAC) and asymmetric algorithms can be tricked into accepting a public JSON Web Key (JWK) as an HMAC secret. This allows an attacker to forge HS256 tokens by using the issuer's public key as the HMAC secret, enabling unauthorized token creation and impersonation. The vulnerability arises because the library only blocks asymmetric keys in PEM or SSH format from being used as HMAC secrets, but does not block JSON Web Keys. This flaw requires a misconfiguration of the verifier and is rated with high attack complexity. A fix is available in version 2026.7.1.

References

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