CVE-2026-77987

Description

A server-side request forgery (SSRF) vulnerability was identified in the notebook viewer of GitHub Enterprise Server. The notebook viewer validated the scheme and host of a user-supplied URL but did not validate the port, allowing requests to be directed to internal services listening on other ports of the same appliance. Response bodies were not returned to the requester, but response timing acted as an oracle that allowed instance secrets to be extracted character by character. An extracted secret could then be used in a separate interaction with an internal service to obtain remote code execution on the appliance. Exploitation required network access to the instance and was unauthenticated when private mode was disabled, or required any authenticated user when private mode was enabled. This vulnerability affected GitHub Enterprise Server versions 3.17 through 3.22 and was fixed in versions 3.22.1, 3.21.6, 3.20.8, 3.19.12, 3.18.15, and 3.17.21. This vulnerability was reported through the GitHub Bug Bounty program.

Overview

State: PUBLISHED
Assigner (CNA): GitHub_P
CVSS severity: CRITICAL
CVSS score: 9.3 / 10
CVSS vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N
Effective score: 9.3 / 10 CRITICAL source: CNA overview
CWE(s): CWE-918, CWE-208
Reserved: 2026-08-21
Published: 2026-09-22 20:43 UTC
Last updated: 2026-09-22 20:43 UTC
Source: https://raw.githubusercontent.com/CVEProject/cvelistV5/main/cves/2026/77xxx/CVE-2026-77987.json
Linked Threat: CVE-2026-77987 — GitHub Enterprise Server notebook viewer vulnerable to Server-side request forgery

NVD triage scoring NVD CVE 2.0

Layer NVD adds on top of the CNA's CVE record — published / last-modified timestamps, exploitability / impact subscores, and the FIRST.org EPSS probability that this CVE will be exploited in the wild in the next 30 days.

NVD published: 2026-09-22 21:17:32 UTC
NVD last modified: 2026-09-22 21:17:32 UTC

European Union Vulnerability Database ENISA EUVD

ENISA's official EU repository for curated vulnerability intelligence. Carries a separate identifier (EUVD-YYYY-NNNN) and frequently exposes an earlier-published description + CVSS than NVD does.

EUVD ID: EUVD-2026-84872
Assigner: GitHub_P
Published: Sep 22, 2026, 8:43:53 PM
Updated: Sep 22, 2026, 8:43:53 PM
EUVD base score (CVSS 4.0): 9.3 / 10
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N
EUVD-reported EPSS: 0.0000
Vendors: GitHub
Products: Enterprise Server (3.21.0 <3.21.*)

Enterprise Server (3.17.0 <3.17.*)

Enterprise Server (3.20.0 <3.20.*)

Enterprise Server (3.18.0 <3.18.*)

Enterprise Server (3.22.0 <3.22.*)

Enterprise Server (3.19.0 <3.19.*)
Aliases: GHSA-5p5v-w43x-q8v7

ENISA description: A server-side request forgery (SSRF) vulnerability was identified in the notebook viewer of GitHub Enterprise Server. The notebook viewer validated the scheme and host of a user-supplied URL but did not validate the port, allowing requests to be directed to internal services listening on other ports of the same appliance. Response bodies were not returned to the requester, but response timing acted as an oracle that allowed instance secrets to be extracted character by character. An extracted secret could then be used in a separate interaction with an internal service to obtain remote code execution on the appliance. Exploitation required network access to the instance and was unauthenticated when private mode was disabled, or required any authenticated user when private mode was enabled. This vulnerability affected GitHub Enterprise Server versions 3.17 through 3.22 and was fixed in versions 3.22.1, 3.21.6, 3.20.8, 3.19.12, 3.18.15, and 3.17.21. This vulnerability was reported through the GitHub Bug Bounty program.

EUVD references (6)

Affected products (1)

Vendor	Product	Versions	Platforms
GitHub	Enterprise Server	`3.17.0` (affected), `3.18.0` (affected), `3.19.0` (affected), `3.20.0` (affected), `3.21.0` (affected), `3.22.0` (affected)	—

Vendor references (6)

References embedded in the original CVE record by the assigning CNA.

https://docs.github.com/en/enterprise-server@3.17/admin/release-notes#3.17.21 release-notes
https://docs.github.com/en/enterprise-server@3.18/admin/release-notes#3.18.15 release-notes
https://docs.github.com/en/enterprise-server@3.19/admin/release-notes#3.19.12 release-notes
https://docs.github.com/en/enterprise-server@3.20/admin/release-notes#3.20.8 release-notes
https://docs.github.com/en/enterprise-server@3.21/admin/release-notes#3.21.6 release-notes
https://docs.github.com/en/enterprise-server@3.22/admin/release-notes#3.22.1 release-notes

Web references (0)

DuckDuckGo results ranked by threat-intel / vendor advisory domains. Generated by the 🔎 Find references (web) button above — same flow as the Remediations search.

No web references attached yet.

NVD-tagged references (6)

Reference list NVD curates from the CNA record, vendor advisories, and third-party reports. The tag chips below are NVD's analyst-assigned categories.

https://docs.github.com/en/enterprise-server@3.17/admin/release-notes#3.17.21 product-cna@github.com
https://docs.github.com/en/enterprise-server@3.18/admin/release-notes#3.18.15 product-cna@github.com
https://docs.github.com/en/enterprise-server@3.19/admin/release-notes#3.19.12 product-cna@github.com
https://docs.github.com/en/enterprise-server@3.20/admin/release-notes#3.20.8 product-cna@github.com
https://docs.github.com/en/enterprise-server@3.21/admin/release-notes#3.21.6 product-cna@github.com
https://docs.github.com/en/enterprise-server@3.22/admin/release-notes#3.22.1 product-cna@github.com

Remediations (10)

Remediations are stored against the linked Threat row; the list below is deduplicated across both pages.

CVE-2026-77987: Enterprise Server Remote Code Execution | CVETodo

web:cvetodo.com

CVE-2026-77987 is a CVSS 9.3 Remote Code Execution vulnerability in GitHub Enterprise Server. See exploitation status, patch guidance, and technical details.

2026-09-23 15:15 UTC
Microsoft Exchange CVE-2026-42897 Patch and OWA Mitigation Guide

web:fixitphill.com

Patch Microsoft Exchange CVE - 2026 -42897 with June 2026 security updates, keep EEMS mitigations during rollout, and verify OWA and mail flow.

2026-09-23 15:15 UTC
Security Advisories and Bulletins | Microsoft Learn

web:learn.microsoft.com

Learning path Learn how Microsoft supports secure software development as part of a cybersecurity solution - Training Secure software development means integrating security into each phase of your development lifecycle, from requirements analysis to maintenance. Microsoft provides many services that can help you develop more secure code and deploy a more secure application in the cloud. This ...

2026-09-23 15:15 UTC
Security Update Guide - Microsoft

web:msrc.microsoft.com

The Microsoft Security Response Center (MSRC) investigates all reports of security vulnerabilities affecting Microsoft products and services, and provides the information here as part of the ongoing effort to help you manage security risks and help keep your systems protected.

2026-09-23 15:15 UTC
Security Update Guide - Microsoft Security Response Center

web:msrc.microsoft.com

Security Update Guide - Microsoft Security Response Center

2026-09-23 15:15 UTC
Microsoft Patch Tracker (September 2026): Exploit-Ranked | Senserva

web:senserva.com

Every Microsoft security patch (KB) and the CVEs it fixes, with severity, CVSS, and CISA KEV status. Cross-linked to the CVE reference.

2026-09-23 15:15 UTC
Description of the security update for Office 2016: August 11, 2026 ...

web:support.microsoft.com

Be aware that the update in the Microsoft Download Center applies to the Microsoft Installer (.msi)-based edition of Office 2016. It doesn't apply to the Office 2016 Click-to-Run editions, such as Microsoft Office 365 Home. (See What version of Office am I using?) How to get and install the update Method 1: Microsoft Update This update is available from Microsoft Update. When you turn on ...

2026-09-23 15:15 UTC
SAP Security Patch Day - June 2026

web:support.sap.com

SAP security Patch Day Bulletin This post shares the information on security notes that remediate vulnerabilities discovered in SAP products. SAP strongly recommends that the customer visits the support portal and applies patches on priority to protect their SAP landscape. On 9th of June 2026 , SAP security patch day saw the release of 15 new security notes.

2026-09-23 15:15 UTC
CVE-2026-77987 - GitHub Enterprise Server SSRF Leads to RCE…

web:vulmon.com

GitHub Enterprise Server SSRF Leads to RCE via Port Validation Flaw. An SSRF vulnerability in GitHub Enterprise Server's notebook viewer enables attackers to…

2026-09-23 15:15 UTC
CVE-2026-62878: Patch Windows DNS Server RCE Flaw

web:windowsforum.com

Microsoft published CVE - 2026 -62878 on August 11 as a Windows DNS Server Remote Code Execution Vulnerability, putting systems that run the Windows DNS Server role into the immediate patch -and-verify queue.

2026-09-23 15:15 UTC

AI Forensic Analysis

Only Available for Registered Users. Sign in to view.

Raw JSON

The full cvelistV5 record. Download as CVE-2026-77987.json.

{
  "containers": {
    "cna": {
      "affected": [
        {
          "defaultStatus": "unknown",
          "product": "Enterprise Server",
          "vendor": "GitHub",
          "versions": [
            {
              "changes": [
                {
                  "at": "3.17.21",
                  "status": "unaffected"
                }
              ],
              "lessThan": "3.17.*",
              "status": "affected",
              "version": "3.17.0",
              "versionType": "semver"
            },
            {
              "changes": [
                {
                  "at": "3.18.15",
                  "status": "unaffected"
                }
              ],
              "lessThan": "3.18.*",
              "status": "affected",
              "version": "3.18.0",
              "versionType": "semver"
            },
            {
              "changes": [
                {
                  "at": "3.19.12",
                  "status": "unaffected"
                }
              ],
              "lessThan": "3.19.*",
              "status": "affected",
              "version": "3.19.0",
              "versionType": "semver"
            },
            {
              "changes": [
                {
                  "at": "3.20.8",
                  "status": "unaffected"
                }
              ],
              "lessThan": "3.20.*",
              "status": "affected",
              "version": "3.20.0",
              "versionType": "semver"
            },
            {
              "changes": [
                {
                  "at": "3.21.6",
                  "status": "unaffected"
                }
              ],
              "lessThan": "3.21.*",
              "status": "affected",
              "version": "3.21.0",
              "versionType": "semver"
            },
            {
              "changes": [
                {
                  "at": "3.22.1",
                  "status": "unaffected"
                }
              ],
              "lessThan": "3.22.*",
              "status": "affected",
              "version": "3.22.0",
              "versionType": "semver"
            }
          ]
        }
      ],
      "credits": [
        {
          "lang": "en",
          "type": "finder",
          "value": "Seokchan Yoon"
        },
        {
          "lang": "en",
          "type": "finder",
          "value": "R31n"
        }
      ],
      "descriptions": [
        {
          "lang": "en",
          "supportingMedia": [
            {
              "base64": false,
              "type": "text/html",
              "value": "A server-side request forgery (SSRF) vulnerability was identified in the notebook viewer of GitHub Enterprise Server. The notebook viewer validated the scheme and host of a user-supplied URL but did not validate the port, allowing requests to be directed to internal services listening on other ports of the same appliance. Response bodies were not returned to the requester, but response timing acted as an oracle that allowed instance secrets to be extracted character by character. An extracted secret could then be used in a separate interaction with an internal service to obtain remote code execution on the appliance. Exploitation required network access to the instance and was unauthenticated when private mode was disabled, or required any authenticated user when private mode was enabled. This vulnerability affected GitHub Enterprise Server versions 3.17 through 3.22 and was fixed in versions 3.22.1, 3.21.6, 3.20.8, 3.19.12, 3.18.15, and 3.17.21. This vulnerability was reported through the GitHub Bug Bounty program.<br><br>"
            }
          ],
          "value": "A server-side request forgery (SSRF) vulnerability was identified in the notebook viewer of GitHub Enterprise Server. The notebook viewer validated the scheme and host of a user-supplied URL but did not validate the port, allowing requests to be directed to internal services listening on other ports of the same appliance. Response bodies were not returned to the requester, but response timing acted as an oracle that allowed instance secrets to be extracted character by character. An extracted secret could then be used in a separate interaction with an internal service to obtain remote code execution on the appliance. Exploitation required network access to the instance and was unauthenticated when private mode was disabled, or required any authenticated user when private mode was enabled. This vulnerability affected GitHub Enterprise Server versions 3.17 through 3.22 and was fixed in versions 3.22.1, 3.21.6, 3.20.8, 3.19.12, 3.18.15, and 3.17.21. This vulnerability was reported through the GitHub Bug Bounty program."
        }
      ],
      "impacts": [
        {
          "capecId": "CAPEC-664",
          "descriptions": [
            {
              "lang": "en",
              "value": "CAPEC-664 Server Side Request Forgery"
            }
          ]
        },
        {
          "capecId": "CAPEC-462",
          "descriptions": [
            {
              "lang": "en",
              "value": "CAPEC-462 Cross-Domain Search Timing"
            }
          ]
        }
      ],
      "metrics": [
        {
          "cvssV4_0": {
            "Automatable": "NOT_DEFINED",
            "Recovery": "NOT_DEFINED",
            "Safety": "NOT_DEFINED",
            "attackComplexity": "LOW",
            "attackRequirements": "NONE",
            "attackVector": "NETWORK",
            "baseScore": 9.3,
            "baseSeverity": "CRITICAL",
            "exploitMaturity": "NOT_DEFINED",
            "privilegesRequired": "NONE",
            "providerUrgency": "NOT_DEFINED",
            "subAvailabilityImpact": "NONE",
            "subConfidentialityImpact": "NONE",
            "subIntegrityImpact": "NONE",
            "userInteraction": "NONE",
            "valueDensity": "NOT_DEFINED",
            "vectorString": "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N",
            "version": "4.0",
            "vulnAvailabilityImpact": "HIGH",
            "vulnConfidentialityImpact": "HIGH",
            "vulnIntegrityImpact": "HIGH",
            "vulnerabilityResponseEffort": "NOT_DEFINED"
          },
          "format": "CVSS",
          "scenarios": [
            {
              "lang": "en",
              "value": "GENERAL"
            }
          ]
        }
      ],
      "problemTypes": [
        {
          "descriptions": [
            {
              "cweId": "CWE-918",
              "description": "CWE-918 Server-Side Request Forgery (SSRF)",
              "lang": "en",
              "type": "CWE"
            },
            {
              "cweId": "CWE-208",
              "description": "CWE-208 Observable Timing Discrepancy",
              "lang": "en",
              "type": "CWE"
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-09-22T20:43:53.715Z",
        "orgId": "82327ea3-741d-41e4-88f8-2cf9e791e760",
        "shortName": "GitHub_P"
      },
      "references": [
        {
          "tags": [
            "release-notes"
          ],
          "url": "https://docs.github.com/en/enterprise-server@3.17/admin/release-notes#3.17.21"
        },
        {
          "tags": [
            "release-notes"
          ],
          "url": "https://docs.github.com/en/enterprise-server@3.18/admin/release-notes#3.18.15"
        },
        {
          "tags": [
            "release-notes"
          ],
          "url": "https://docs.github.com/en/enterprise-server@3.19/admin/release-notes#3.19.12"
        },
        {
          "tags": [
            "release-notes"
          ],
          "url": "https://docs.github.com/en/enterprise-server@3.20/admin/release-notes#3.20.8"
        },
        {
          "tags": [
            "release-notes"
          ],
          "url": "https://docs.github.com/en/enterprise-server@3.21/admin/release-notes#3.21.6"
        },
        {
          "tags": [
            "release-notes"
          ],
          "url": "https://docs.github.com/en/enterprise-server@3.22/admin/release-notes#3.22.1"
        }
      ],
      "source": {
        "discovery": "EXTERNAL"
      },
      "title": "GitHub Enterprise Server notebook viewer vulnerable to Server-side request forgery",
      "x_generator": {
        "engine": "Vulnogram 0.2.0"
      }
    }
  },
  "cveMetadata": {
    "assignerOrgId": "82327ea3-741d-41e4-88f8-2cf9e791e760",
    "assignerShortName": "GitHub_P",
    "cveId": "CVE-2026-77987",
    "datePublished": "2026-09-22T20:43:53.715Z",
    "dateReserved": "2026-08-21T18:51:48.052Z",
    "dateUpdated": "2026-09-22T20:43:53.715Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}