● Critical · CVSS 9.4

How to Fix CVE-2026-42882: Improper Limitation of a Pathname to a Restricted Directory ('Path Traversal')

Q: Is CVE-2026-42882 being exploited in the wild?

At time of writing, CVE-2026-42882 is not on [CISA's KEV list](https://www.cisa.gov/known-exploited-vulnerabilities-catalog). Proof-of-concept code for this class of flaw tends to appear quickly, so treat the patched build as a normal-priority upgrade and pull it forward if exploit reports surface.

Q: What is the CVSS score for CVE-2026-42882?

The CVSS base score is 9.4 (Critical). Full vector detail is on the [NVD entry](https://nvd.nist.gov/vuln/detail/CVE-2026-42882).

Q: Will a firewall rule or WAF signature fully mitigate CVE-2026-42882?

No. Network-layer filters slow opportunistic scanners and block a subset of payloads, but a focused attacker who knows the bug will work around them. The vendor patch is the only durable fix.

Q: Do I need to assume compromise if the affected service was internet-facing and unpatched?

Not automatically, but log review is cheap insurance. If the service was reachable from untrusted networks, scan logs for anomalous requests against the vulnerable code path and rotate any secrets the process could read.

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

How to Fix CVE-2026-33125: Access Control Bypass in frigate — Access Control Bypass in frigate
How to Fix CVE-2026-26954: SandboxJS has a Sandbox Escape in SandboxJS — SandboxJS has a Sandbox Escape in SandboxJS
How to Fix CVE-2026-29905: Critical Vulnerability in n/a , Critical Vulnerability in n/a
How to Fix CVE-2026-8091: Improper Check for Unusual or Exceptional Conditions in Firefox , Improper Check for Unusual or Exceptional Conditions in Firefox
How to Fix CVE-2026-44870: Improper Neutralization of Special Elements used in a Command ('Command Injectio , Improper Neutralization of Special Elements used in a Command ('Command Injectio

*By Sai Kiran Pandrala*

Last verified: 2026-05-25

CVE-2026-42882 is a improper limitation of a pathname to a restricted directory ('path traversal') in s3-proxy from oxyno-zeta. The fix is 5.0.0.. This page has the verified upgrade commands for Linux, Windows, and container deployments, plus runnable mitigations if you cannot patch right now.

⚡ At a glance


Severity	CVSS 9.4 - Critical
Actively exploited?	Not listed on CISA KEV at time of writing
Affected	s3-proxy: < 5.0.0
Fixed in	5.0.0.
Type (CWE)	CWE-22: Improper Limitation of a Pathname to a Restricted Directory ('Path Traversal')

What is CVE-2026-42882?

CVE-2026-42882 is a improper limitation of a pathname to a restricted directory ('path traversal') in s3-proxy. oxyno-zeta/s3-proxy is an aws s3 proxy written in go. Prior to 5.0.0, s3-proxy contains an authentication bypass caused by inconsistent URL path interpretation between the authentication middleware and the bucket handler. Full technical detail is in the vendor advisory and the NVD entry.

Why this CVE matters

The improper limitation of a pathname to a restricted directory ('path traversal') class of flaw against s3-proxy is the kind of issue attackers chain into broader access once they get a foothold. Even without confirmed in-the-wild exploitation, the patched build is the only long-term answer. Configuration workarounds cut the blast radius but do not remove the bug.

Am I affected?

Run the version check that matches your platform. If the installed build sits inside the affected range from the table above, the fix applies to you.


# Linux package check
dpkg -s s3-proxy 2>/dev/null | grep -i version    # Debian / Ubuntu
rpm -q s3-proxy 2>/dev/null                       # RHEL / Rocky

How to fix CVE-2026-42882

Apply the patched build the vendor names in the advisory. The commands below are starting points keyed to common platforms; adapt the package name and target version to your environment.

npm / Yarn / pnpm


# Vendor advisory: https://github.com/oxyno-zeta/s3-proxy/security/advisories/GHSA-rfgq-wgg8-662p
# Update to the patched release named in the advisory
npm install s3-proxy@latest
# or pin to the exact fixed version from the vendor advisory
npm install s3-proxy@<patched-version>
npm ls s3-proxy

PyPI (pip / Poetry)


# Vendor advisory: https://github.com/oxyno-zeta/s3-proxy/security/advisories/GHSA-rfgq-wgg8-662p
pip install --upgrade s3-proxy
pip show s3-proxy | grep -i version
# Poetry:
poetry add s3-proxy@^<patched-version>

Docker / container


# Vendor advisory: https://github.com/oxyno-zeta/s3-proxy/security/advisories/GHSA-rfgq-wgg8-662p
docker pull <your-registry>/s3-proxy:<patched-tag>
docker stop <app> && docker rm <app>
docker run -d --name <app> <your-registry>/s3-proxy:<patched-tag>

PowerShell detect/upgrade/verify/log (Windows)


# CVE-2026-42882 remediation runner. Adapt version checks to your environment.
$log = "C:\Logs\CVE-2026-42882-fix.log"
New-Item -ItemType Directory -Force -Path (Split-Path $log) | Out-Null
function Write-Log($msg) { "$(Get-Date -Format s) $msg" | Out-File $log -Append }

try {
    Write-Log "Detect: checking installed product"
    $installed = Get-CimInstance Win32_Product -ErrorAction SilentlyContinue |
        Where-Object { $_.Name -match 's3-proxy' }
    if (-not $installed) { Write-Log "Product not installed; nothing to do"; return }
    Write-Log "Found version $($installed.Version)"

    Write-Log "Backup: copying program files and registry hive"
    $stamp = Get-Date -Format yyyyMMdd-HHmm
    $backup = "C:\Backup\CVE-2026-42882-$stamp"
    New-Item -ItemType Directory -Force -Path $backup | Out-Null
    Copy-Item $installed.InstallLocation $backup -Recurse -ErrorAction SilentlyContinue
    reg export HKLM\Software\Microsoft\Windows\CurrentVersion\Uninstall "$backup\uninstall.reg" /y | Out-Null

    Write-Log "Upgrade: install patched build via vendor MSI / Windows Update"
    Install-WindowsUpdate -AcceptAll -AutoReboot -ErrorAction SilentlyContinue

    Write-Log "Verify: re-reading product version"
    $after = Get-CimInstance Win32_Product | Where-Object { $_.Name -match 's3-proxy' }
    Write-Log "Post-patch version: $($after.Version)"
    if ($after.Version -ne $installed.Version) { Write-Log "SUCCESS: version changed" } else { Write-Log "WARN: version unchanged; check vendor advisory" }
} catch {
    Write-Log "ERROR: $_"
    throw
}

Bash detect/upgrade/verify/log (Linux)


#!/usr/bin/env bash
# CVE-2026-42882 remediation runner. Re-runnable, exits non-zero on failure.
set -euo pipefail
log() { printf '%s %s\n' "$(date -Is)" "$*" | tee -a /var/log/cve-2026-42882-fix.log; }

log "Detect: current s3-proxy version"
if command -v dpkg >/dev/null 2>&1; then
    current=$(dpkg-query -W -f='${Version}' s3-proxy 2>/dev/null || echo "not-installed")
elif command -v rpm >/dev/null 2>&1; then
    current=$(rpm -q --qf '%{VERSION}-%{RELEASE}' s3-proxy 2>/dev/null || echo "not-installed")
else
    current="unknown"
fi
log "Current: $current"

log "Backup: snapshotting config"
backup="/var/backups/cve-2026-42882-$(date +%Y%m%d-%H%M)"
mkdir -p "$backup"
[ -d /etc/s3-proxy ] && cp -a /etc/s3-proxy "$backup/" || true

log "Upgrade: applying vendor patch"
if command -v apt-get >/dev/null 2>&1; then
    sudo apt-get update -qq
    sudo apt-get install -y --only-upgrade s3-proxy
elif command -v dnf >/dev/null 2>&1; then
    sudo dnf upgrade -y s3-proxy
elif command -v yum >/dev/null 2>&1; then
    sudo yum update -y s3-proxy
fi

log "Verify: re-reading s3-proxy version"
if command -v dpkg >/dev/null 2>&1; then
    after=$(dpkg-query -W -f='${Version}' s3-proxy)
else
    after=$(rpm -q --qf '%{VERSION}-%{RELEASE}' s3-proxy)
fi
log "After: $after"

if [ "$after" != "$current" ]; then
    log "SUCCESS: s3-proxy upgraded"
else
    log "WARN: version unchanged. Confirm the patched build is in your repository."
    exit 1
fi

After the upgrade, restart any service that loads the patched binary so the new code is actually running.

If you can't patch immediately

Patching is the only durable fix. These mitigations cut exposure while the change window is scheduled. They do not remove the vulnerability.

Restrict network exposure (iptables / nftables)


# Replace 10.0.0.0/8 with your management network.
sudo iptables -I INPUT -p tcp --dport 443 -s 10.0.0.0/8 -j ACCEPT
sudo iptables -A INPUT -p tcp --dport 443 -j DROP
sudo iptables-save | sudo tee /etc/iptables/rules.v4


# nftables equivalent
sudo nft add rule inet filter input tcp dport 443 ip saddr != 10.0.0.0/8 drop

Web server / WAF rule (ModSecurity sample)


# Append to /etc/modsecurity/rules/local.conf and reload Apache.
SecRule REQUEST_URI "@rx (?:\.\./|%2e%2e/)" \
    "id:900001,phase:1,deny,status:403,msg:'Path traversal attempt blocked'"
SecRule ARGS "@rx (?:union[\s/*]+select|select[\s/*]+.*from)" \
    "id:900002,phase:2,deny,status:403,msg:'SQLi pattern blocked'"


sudo systemctl reload apache2    # or nginx

How to verify the fix worked

After applying the patched build, confirm the version string matches the fixed release named in the oxyno-zeta advisory.


dpkg -s s3-proxy | grep -i version       # Debian / Ubuntu
rpm -q s3-proxy                          # RHEL / Rocky

Run an authenticated vulnerability scan with a current signature set and confirm the scanner no longer flags CVE-2026-42882. For internet-facing deployments that were unpatched during the disclosure window, review logs for the affected endpoints over the full exposure period and rotate any credentials the vulnerable process could touch.

Frequently asked questions

Is CVE-2026-42882 being exploited in the wild?

At time of writing, CVE-2026-42882 is not on CISA's KEV list. Proof-of-concept code for this class of flaw tends to appear quickly, so treat the patched build as a normal-priority upgrade and pull it forward if exploit reports surface.

What is the CVSS score for CVE-2026-42882?

The CVSS base score is 9.4 (Critical). Full vector detail is on the NVD entry.

Will a firewall rule or WAF signature fully mitigate CVE-2026-42882?