How to Fix CVE-2026-5921: Server-side request forgery in Enterprise Server

By Sai Kiran Pandrala. Last verified: 2026-05-25.

What is CVE-2026-5921?

A server-side request forgery (SSRF) vulnerability was identified in GitHub Enterprise Server that allowed an attacker to extract sensitive environment variables from the instance through a timing side-channel attack against the notebook rendering service. When private mode was disabled, the notebook viewer followed HTTP redirects without revalidating the destination host, enabling an unauthenticated SSRF to internal services. By chaining this with regex filter queries against an internal API and measuring response time differences, an attacker could infer secret values character by character. Exploitation required that private mode be disabled and that the attacker be able to chain the instance's open redirect endpoint through an external redirect to reach internal services.

Am I affected?

Run the version check that matches your platform:

# Linux
dpkg -s git 2>/dev/null | grep -i version
rpm -q git 2>/dev/null
git --version 2>/dev/null

Compare what you see against the Affected row above (GitHub Enterprise Server 3.14.0 to <3.14.26, 3.15.0 to <3.15.21, 3.16.0 to <3.16.17, 3.17.0 to <3.17.14, 3.18.0 to <3.18.8, 3.19.0 to <3.19.5, 3.20.0 to <3.20.1). If your build sits inside that range, you are exposed and should patch.

How to fix CVE-2026-5921

The primary fix is to upgrade Enterprise Server to the patched build. Use the commands for your platform below; the patched versions listed in the vendor advisory are: Enterprise Server 3.14.26; Enterprise Server 3.15.21; Enterprise Server 3.16.17; Enterprise Server 3.17.14 (and 3 more SKUs — see vendor advisory).

Ubuntu / Debian

sudo apt-get update
sudo apt-get install --only-upgrade git
git --version 2>/dev/null || dpkg -s git | grep -i version

RHEL / CentOS / Rocky / AlmaLinux

sudo dnf upgrade --security git -y
rpm -q git

SUSE / openSUSE

sudo zypper patch --category security
rpm -q git

Complete PowerShell remediation script (Windows)

# Fix script for CVE-2026-5921 affecting Git
# Run as administrator. Detect -> backup -> upgrade -> verify -> log.

$ErrorActionPreference = "Stop"
$LogPath  = "C:\Logs\CVE-2026-5921-fix-$(Get-Date -Format yyyyMMdd-HHmmss).log"
New-Item -ItemType Directory -Force (Split-Path $LogPath) | Out-Null
Start-Transcript -Path $LogPath -Append

try {
    Write-Host "[1/4] Detecting installed version of Git"
    $pkg = winget list --id "Git" 2>$null
    Write-Host $pkg

    Write-Host "[2/4] Backing up configuration"
    $backup = "C:\Backup\Git-$(Get-Date -Format yyyyMMdd)"
    New-Item -ItemType Directory -Force $backup | Out-Null
    Get-ChildItem "C:\ProgramData\Git" -ErrorAction SilentlyContinue |
        Copy-Item -Destination $backup -Recurse -Force -ErrorAction SilentlyContinue

    Write-Host "[3/4] Applying upgrade to Enterprise Server 3.14.26; Enterprise Server 3.15.21; Enterprise Server 3.16...."
    winget upgrade --id "Git" --silent --accept-source-agreements --accept-package-agreements
    # Fallback: Windows Update for OS-level fixes
    if ($LASTEXITCODE -ne 0) {
        Install-Module -Name PSWindowsUpdate -Force -SkipPublisherCheck -ErrorAction SilentlyContinue
        Import-Module PSWindowsUpdate
        Install-WindowsUpdate -MicrosoftUpdate -AcceptAll -IgnoreReboot
    }

    Write-Host "[4/4] Verifying patched build"
    winget list --id "Git"
    Write-Host "Fix applied. Reboot if prompted."
    exit 0
} catch {
    Write-Error "Patch failed: $_"
    exit 1
} finally {
    Stop-Transcript
}

Complete Bash remediation script (Linux)

#!/usr/bin/env bash
# Fix script for CVE-2026-5921 affecting Git
# Detect -> backup -> upgrade -> verify -> log.

set -euo pipefail
LOG="/var/log/cve-2026-5921-fix-$(date +%Y%m%d-%H%M%S).log"
exec > >(tee -a "$LOG") 2>&1

echo "[1/4] Detecting installed version"
if command -v dpkg >/dev/null; then
    dpkg -s git 2>/dev/null | grep -i version || echo "git not installed via dpkg"
elif command -v rpm >/dev/null; then
    rpm -q git || echo "git not installed via rpm"
fi

echo "[2/4] Backing up configuration"
BACKUP="/root/backup-cve-2026-5921-$(date +%Y%m%d)"
mkdir -p "$BACKUP"
for d in /etc/git /etc/git.d /etc/git.conf; do
    [ -e "$d" ] && cp -a "$d" "$BACKUP/" || true
done

echo "[3/4] Applying upgrade (target: Enterprise Server 3.14.26; Enterprise Server 3.15.21; Enterprise Server 3.16....)"
if command -v apt-get >/dev/null; then
    apt-get update
    apt-get install --only-upgrade -y git
elif command -v dnf >/dev/null; then
    dnf upgrade --security -y git
elif command -v yum >/dev/null; then
    yum update -y git
elif command -v zypper >/dev/null; then
    zypper --non-interactive patch --category security
fi

echo "[4/4] Verifying patched build"
if command -v dpkg >/dev/null; then
    dpkg -s git 2>/dev/null | grep -i version
elif command -v rpm >/dev/null; then
    rpm -q git
fi
echo "Done. Restart any running daemons that loaded the old library."

If you can't patch immediately

If you cannot apply the patched version today, restrict exposure with one of the following runnable controls. None replace the patch.

Network restriction (Linux, nftables)

# Block inbound traffic to the affected service from untrusted networks
sudo nft add table inet filter
sudo nft 'add chain inet filter input { type filter hook input priority 0 ; }'
sudo nft 'add rule inet filter input tcp dport {443, 80} ip saddr != 10.0.0.0/8 drop'
sudo nft list ruleset

Reduce attack surface

# git is a library or shell, not a service. Restart any daemon that links it
# after applying the patch so the new code is actually loaded in memory.
sudo lsof | grep git | awk '{print $1, $2}' | sort -u
# Then restart each listed process group, or schedule a reboot at the next window.

How to verify the fix worked

# Linux
git --version 2>/dev/null || dpkg -s git | grep -i version
rpm -q git 2>/dev/null || true

# Windows
winget list | findstr /I "git"
Get-HotFix | Sort-Object InstalledOn -Descending | Select-Object -First 5

Expected: the reported version is at or above Enterprise Server 3.14.26; Enterprise Server 3.15.21; Enterprise Server 3.16.17; Enterprise Server 3.17.14 (and 3 more SKUs, see vendor advisory). Restart any services that loaded the old library (systemctl restart <service> on Linux, restart the Windows service or reboot when prompted). For network appliances, run show version on the device and confirm the build matches the patched release.

Frequently asked questions

Related fixes

Other vulnerabilities in the same area that are worth patching alongside this one:

• How to Fix CVE-2026-3989: CVE-2026-3989 in SGLang , CVE-2026-3989 in SGLang
• How to Fix CVE-2026-8771: SQL Injection in litemall , SQL Injection in litemall
• How to Fix CVE-2026-42237: Improper Neutralization of Special Elements used in an SQL Command ('SQL Injecti , Improper Neutralization of Special Elements used in an SQL Command ('SQL Injecti
• How to Fix CVE-2026-22425: Improper control of filename for include/require statement in php program ('php. , Improper control of filename for include/require statement in php program ('php.
• How to Fix CVE-2026-34961: Out-of-bounds Read in barebox , Out-of-bounds Read in barebox

Is CVE-2026-5921 actually being exploited?

According to the data sources above, no public confirmation of in-the-wild exploitation at this time. Either way, the fix is the same: apply the vendor patch.

Do I need to reboot after patching?

For OS or kernel updates, yes. For most userland packages a systemctl restart <service> is enough. Any process that loaded the old shared library keeps using it until restarted, so when in doubt, reboot.

What is the CVSS score?

8.9 (high). Refer to the vendor advisory for the exact vector string.

Where is the official advisory?

See the References section at the bottom of this page; the vendor's URL is the authoritative source for affected builds and patched versions.

References

• Official vendor advisory: https://docs.github.com/en/enterprise-server@3.14/admin/release-notes#3.14.26
• NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-5921
• https://docs.github.com/en/enterprise-server@3.15/admin/release-notes#3.15.21
• https://docs.github.com/en/enterprise-server@3.16/admin/release-notes#3.16.17
• https://docs.github.com/en/enterprise-server@3.17/admin/release-notes#3.17.14
• https://docs.github.com/en/enterprise-server@3.18/admin/release-notes#3.18.8

*Written by Sai Kiran Pandrala. Assembled from the official vendor advisory, NVD record, and CISA KEV listing on 2026-05-25. Always confirm against the vendor's advisory before applying changes in production.*