CVE-2026-49955Network attack vectorHinoki check available

Service degradation via unbounded passkey challenge storage

Published Jun 9, 2026 · Updated Jun 9, 2026

Resource exhaustion in Hermes WebUI before 0.51.270 allows remote attackers to degrade login availability via unauthenticated passkey requests. The public POST /api/auth/passkey/options handler mints a challenge for every request, and _store_challenge() appends it to .passkey_challenges.json before rewriting the whole uncapped file. Auth and passkeys must be enabled with a credential registered; repeated requests without completed assertions drive file growth and excessive CPU and disk I/O.

CVSS severity6.9
Medium
EPSS probability0.59%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkAvailable
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Summary

What happened

Resource exhaustion in Hermes WebUI before 0.51.270 allows remote attackers to degrade login availability via unauthenticated passkey requests. The public POST /api/auth/passkey/options handler mints a challenge for every request, and _store_challenge() appends it to .passkey_challenges.json before rewriting the whole uncapped file. Auth and passkeys must be enabled with a credential registered; repeated requests without completed assertions drive file growth and excessive CPU and disk I/O.

The record

CVE
CVE-2026-49955
Published
Jun 9, 2026
Updated
Jun 9, 2026
Vendor
Nathan Esquenazi
Product
Hermes WebUI
Classifications
CWE-770, T1499.003
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jun 9, 2026CVE publishedPublication date reported by the CVE source.
  2. Jun 9, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=0 <0.51.270

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Nathan Esquenazi · Hermes WebUIversion=0 <0.51.270

Published CVSS scores

6.9VulnCheckCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N
5.3VulnCheckCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 9, 2026Sep 15, 2026
Latest reporting daySep 15, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-770Allocation of Resources Without Limits or Throttling
T1499.003Application Exhaustion Flood

Public exploit references

No public exploit references are available in this record.

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Technologies

Your stack

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Your stack

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