CVE-2026-55549Public exploitNetwork attack vector

Account takeover via unescaped authorization redirect

Published Aug 28, 2026 · Updated Aug 28, 2026

Reflected XSS in Yamcs before 5.9.4 allows remote attackers to execute JavaScript in a user's browser through a crafted authorization URL. AuthHandler and HandlerContext place redirect_uri from GET /auth/authorize into authorize.html without adequate HTML escaping. A Yamcs user must open the crafted URL; the script can steal browser-held session and refresh tokens, enabling account takeover.

CVSS severity6.5
Medium
EPSS probability0.36%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Reflected XSS in Yamcs before 5.9.4 allows remote attackers to execute JavaScript in a user's browser through a crafted authorization URL. AuthHandler and HandlerContext place redirect_uri from GET /auth/authorize into authorize.html without adequate HTML escaping. A Yamcs user must open the crafted URL; the script can steal browser-held session and refresh tokens, enabling account takeover.

The record

CVE
CVE-2026-55549
Published
Aug 28, 2026
Updated
Aug 28, 2026
Vendor
Space Applications Services
Product
Yamcs
Classifications
CWE-79, T1203, T1539
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Aug 28, 2026CVE publishedPublication date reported by the CVE source.
  2. Aug 28, 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=< 5.9.4

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Space Applications Services · Yamcsversion=< 5.9.4

Published CVSS scores

6.5GitHubCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:N/A: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 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-79Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
T1203Exploitation for Client Execution
T1539Steal Web Session Cookie

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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