CVE-2026-28508Public exploitNetwork attack vector

Unauthenticated SSRF via premature API request flag

Published Mar 6, 2026 · Updated Mar 6, 2026

SSRF in the URL unfurl service in Known before 1.6.4 allows remote attackers to read arbitrary HTTP responses through the server. Session::tryAuthUser() marks requests as API traffic before HMAC verification, so fabricated authentication headers make token validation return true; UnfurledUrl::unfurl() then fetches any syntactically valid URL without restricting private, loopback, or link-local destinations. No account or user interaction is required, and reachable internal HTTP services or cloud metadata can have response content disclosed.

CVSS severity9.2
Critical
EPSS probability0.63%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

SSRF in the URL unfurl service in Known before 1.6.4 allows remote attackers to read arbitrary HTTP responses through the server. Session::tryAuthUser() marks requests as API traffic before HMAC verification, so fabricated authentication headers make token validation return true; UnfurledUrl::unfurl() then fetches any syntactically valid URL without restricting private, loopback, or link-local destinations. No account or user interaction is required, and reachable internal HTTP services or cloud metadata can have response content disclosed.

The record

CVE
CVE-2026-28508
Published
Mar 6, 2026
Updated
Mar 6, 2026
Vendor
Known, Inc.
Product
Known
Classifications
CWE-918, T1190
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Mar 6, 2026CVE publishedPublication date reported by the CVE source.
  2. Mar 6, 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=< 1.6.4

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Known, Inc. · Knownversion=< 1.6.4

Published CVSS scores

9.2GitHubCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:N/VA:N/SC:H/SI:N/SA:N

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.

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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 exploitPublished

Weakness, pattern, technique

CWE-918Server-Side Request Forgery (SSRF)
T1190Exploit Public-Facing Application

Public exploit references

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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