● Medium · CVSS 5.9

How to Fix CVE-2026-5295: Stack buffer overflow in wolfSSL

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

⚡ At a glance


Severity	5.9 (Medium)
Actively exploited?	No public listing in CISA KEV
Affected	wolfSSL 0 to <5.9.1
Fixed in	wolfSSL 5.9.1
Type (CWE)	CWE-121: Stack-based Buffer Overflow

What is CVE-2026-5295?

A stack buffer overflow exists in wolfSSL's PKCS7 implementation in the wc_PKCS7_DecryptOri() function in wolfcrypt/src/pkcs7.c. When processing a CMS EnvelopedData message containing an OtherRecipientInfo (ORI) recipient, the function copies an ASN.1-parsed OID into a fixed 32-byte stack buffer (oriOID[MAX_OID_SZ]) via XMEMCPY without first validating that the parsed OID length does not exceed MAX_OID_SZ. A crafted CMS EnvelopedData message with an ORI recipient containing an OID longer than 32 bytes triggers a stack buffer overflow. Exploitation requires the library to be built with --enable-pkcs7 (disabled by default) and the application to have registered an ORI decrypt callback via wc_PKCS7_SetOriDecryptCb().

Am I affected?

Run the version check that matches your platform:


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

Compare what you see against the Affected row above (wolfSSL 0 to <5.9.1). If your build sits inside that range, you are exposed and should patch.

How to fix CVE-2026-5295

The primary fix is to upgrade wolfSSL to the patched build. Use the commands for your platform below; the patched version listed in the vendor advisory is: wolfSSL 5.9.1.

Ubuntu / Debian


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

RHEL / CentOS / Rocky / AlmaLinux


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

SUSE / openSUSE


sudo zypper patch --category security
rpm -q wolfssl

Complete PowerShell remediation script (Windows)


# Fix script for CVE-2026-5295 affecting wolfSSL
# Run as administrator. Detect -> backup -> upgrade -> verify -> log.

$ErrorActionPreference = "Stop"
$LogPath  = "C:\Logs\CVE-2026-5295-fix-$(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 wolfSSL"
    $pkg = winget list --id "wolfSSL" 2>$null
    Write-Host $pkg

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

    Write-Host "[3/4] Applying upgrade to wolfSSL 5.9.1"
    winget upgrade --id "wolfSSL" --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 "wolfSSL"
    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-2026-5295 affecting wolfSSL
# Detect -> backup -> upgrade -> verify -> log.

set -euo pipefail
LOG="/var/log/cve-2026-5295-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 wolfssl 2>/dev/null | grep -i version || echo "wolfssl not installed via dpkg"
elif command -v rpm >/dev/null; then
    rpm -q wolfssl || echo "wolfssl not installed via rpm"
fi

echo "[2/4] Backing up configuration"
BACKUP="/root/backup-cve-2026-5295-$(date +%Y%m%d)"
mkdir -p "$BACKUP"
for d in /etc/wolfssl /etc/wolfssl.d /etc/wolfssl.conf; do
    [ -e "$d" ] && cp -a "$d" "$BACKUP/" || true
done

echo "[3/4] Applying upgrade (target: wolfSSL 5.9.1)"
if command -v apt-get >/dev/null; then
    apt-get update
    apt-get install --only-upgrade -y wolfssl
elif command -v dnf >/dev/null; then
    dnf upgrade --security -y wolfssl
elif command -v yum >/dev/null; then
    yum update -y wolfssl
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 wolfssl 2>/dev/null | grep -i version
elif command -v rpm >/dev/null; then
    rpm -q wolfssl
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

Service-level fallback


# If the affected feature is optional, stop the service until the patch is applied
sudo systemctl stop wolfssl
sudo systemctl disable wolfssl

How to verify the fix worked


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


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

Expected: the reported version is at or above wolfSSL 5.9.1. 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

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

How to Fix CVE-2026-5448: wolfSSL (Bundle Sibling) — wolfSSL (Bundle Sibling)
How to Fix CVE-2026-0930: Buffer over-read in wolfSSH — Buffer over-read in wolfSSH
How to Fix CVE-2026-2646: Heap buffer overflow in session parsing with wolfSSL_d2i_SSL_SESSION() function , Heap buffer overflow in session parsing with wolfSSL_d2i_SSL_SESSION() function
How to Fix CVE-2026-5466: Verification of cryptographic signature in wolfSSL , Verification of cryptographic signature in wolfSSL
How to Fix CVE-2026-5477: Integer overflow in wolfSSL , Integer overflow in wolfSSL

Is CVE-2026-5295 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?

5.9 (medium). 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://github.com/wolfSSL/wolfssl/pull/10116
NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-5295

*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.*