● Medium · CVSS 6.5

How to Fix CVE-2026-3255: Cwe-340 generation of predictable numbers or identifiers in HTTP::Session2

Q: What is the CVSS score for CVE-2026-3255?

6.5 (Medium). Vector: `CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:L`.

Q: Where is the official advisory for CVE-2026-3255?

The vendor advisory is at [https://metacpan.org/release/TOKUHIROM/HTTP-Session2-1.11/source/lib/HTTP/Session2/Random.pm#L35](https://metacpan.org/release/TOKUHIROM/HTTP-Session2-1.11/source/lib/HTTP/Session2/Random.pm#L35). The NVD record is at https://nvd.nist.gov/vuln/detail/CVE-2026-3255.

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

CVE-2026-3255 is a cwe-340 generation of predictable numbers or identifiers in TOKUHIROM HTTP::Session2. The fix is to apply the vendor patch noted below.

⚡ At a glance


Severity	6.5 (Medium)
Actively exploited?	No public listing in CISA KEV
Affected	HTTP::Session2 0 to <1.12
Fixed in	See vendor advisory
Type (CWE)	CWE-340 Generation of Predictable Numbers or Identifiers

What is CVE-2026-3255?

HTTP::Session2 versions before 1.12 for Perl for Perl may generate weak session ids using the rand() function.

The HTTP::Session2 session id generator returns a SHA-1 hash seeded with the built-in rand function, the epoch time, and the PID. The PID will come from a small set of numbers, and the epoch time may be guessed, if it is not leaked from the HTTP Date header. The built-in rand() function is unsuitable for cryptographic usage.

HTTP::Session2 after version 1.02 will attempt to use the /dev/urandom device to generate a session id, but if the device is unavailable (for example, under Windows), then it will revert to the insecure method described above. The CVSS base score is 6.5 (Medium). The official advisory is at https://metacpan.org/release/TOKUHIROM/HTTP-Session2-1.11/source/lib/HTTP/Session2/Random.pm#L35.

Am I affected?

Check the version of HTTP::Session2 you are running and compare it against the Affected row above (HTTP::Session2 0 to <1.12). If your build sits inside the affected range, you must patch.

Run the version check that fits your platform:


# Linux package check
dpkg -s http-session2 2>/dev/null | grep -i ^Version
rpm -q http-session2 2>/dev/null
command -v http-session2 >/dev/null && http-session2 --version 2>/dev/null


# Windows (PowerShell)
Get-Package -Name "*HTTP::Session2*" -ErrorAction SilentlyContinue | Select-Object Name, Version
winget list --name "HTTP::Session2" 2>$null

How to fix CVE-2026-3255

Upgrade HTTP::Session2 to a patched build: See vendor advisory. The vendor advisory is the source of truth for the exact fixed version.

Ubuntu / Debian


sudo apt-get update
sudo apt-get install --only-upgrade http-session2
dpkg -s http-session2 | grep -i ^Version

RHEL / CentOS / Rocky / AlmaLinux


sudo dnf upgrade --refresh http-session2 -y
# or for older releases:
sudo yum update http-session2 -y
rpm -q http-session2

SUSE / openSUSE


sudo zypper refresh
sudo zypper update http-session2
rpm -q http-session2

Node.js / npm


# Update the affected package in your project
npm install HTTP::Session2@latest
npm ls HTTP::Session2
npm audit fix

Complete PowerShell remediation script (Windows)


# Fix script for CVE-2026-3255 affecting HTTP::Session2
# Run as administrator. Detect -> backup -> upgrade -> verify -> log.

$ErrorActionPreference = "Stop"
$LogPath  = "C:\Logs\CVE-2026-3255-fix-$(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] Detect installed version"
    $pkg = Get-Package -Name "*HTTP::Session2*" -ErrorAction SilentlyContinue
    if ($pkg) { $pkg | Format-Table Name, Version }
    else { Write-Host "Not detected via Get-Package; try winget list" }

    Write-Host "[2/4] Backup configuration"
    $backup = "C:\Backup\http-session2-$(Get-Date -Format yyyyMMdd)"
    New-Item -ItemType Directory -Force $backup | Out-Null
    Get-ChildItem "C:\ProgramData\HTTP::Session2" -ErrorAction SilentlyContinue |
        Copy-Item -Destination $backup -Recurse -Force -ErrorAction SilentlyContinue

    Write-Host "[3/4] Apply the upgrade to See vendor advisory"
    winget upgrade --name "HTTP::Session2" --silent --accept-source-agreements --accept-package-agreements
    if ($LASTEXITCODE -ne 0) {
        # Fallback: pull latest via OS update channel
        Install-Module -Name PSWindowsUpdate -Force -SkipPublisherCheck -ErrorAction SilentlyContinue
        Import-Module PSWindowsUpdate
        Install-WindowsUpdate -MicrosoftUpdate -AcceptAll -IgnoreReboot
    }

    Write-Host "[4/4] Verify the patched build"
    winget list --name "HTTP::Session2"
    Write-Host "Patch 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-2026-3255 affecting HTTP::Session2
# Detect -> backup -> upgrade -> verify -> log.

set -euo pipefail
LOG="/var/log/cve-2026-3255-fix-$(date +%Y%m%d-%H%M%S).log"
exec > >(tee -a "$LOG") 2>&1

echo "[1/4] Detect installed version"
if command -v dpkg >/dev/null; then
    dpkg -s http-session2 2>/dev/null | grep -i ^Version || echo "http-session2 not installed via dpkg"
elif command -v rpm >/dev/null; then
    rpm -q http-session2 || echo "http-session2 not installed via rpm"
fi

echo "[2/4] Backup configuration"
BACKUP="/root/backup-cve-2026-3255-$(date +%Y%m%d)"
mkdir -p "$BACKUP"
for d in /etc/http-session2 /etc/http-session2.d /etc/http-session2.conf; do
    [ -e "$d" ] && cp -a "$d" "$BACKUP/" || true
done

echo "[3/4] Apply the upgrade (target: See vendor advisory)"
if command -v apt-get >/dev/null; then
    apt-get update
    apt-get install --only-upgrade -y http-session2
elif command -v dnf >/dev/null; then
    dnf upgrade --refresh -y http-session2
elif command -v yum >/dev/null; then
    yum update -y http-session2
elif command -v zypper >/dev/null; then
    zypper --non-interactive update http-session2
fi

echo "[4/4] Verify the patched build"
if command -v dpkg >/dev/null; then
    dpkg -s http-session2 2>/dev/null | grep -i ^Version
elif command -v rpm >/dev/null; then
    rpm -q http-session2
fi
echo "Done. Restart any service that loaded the old library."

If you can't patch immediately

Apply at least one of the following inline controls until you can deploy the patched build. None replace the upgrade.

Restrict exposure with nftables (Linux)


# Allow only trusted CIDR to reach the affected service ports
sudo nft add table inet filter 2>/dev/null || true
sudo nft 'add chain inet filter input { type filter hook input priority 0 ; }' 2>/dev/null || true
sudo nft 'add rule inet filter input tcp dport {80, 443} ip saddr != 10.0.0.0/8 drop'
sudo nft list ruleset

Block at the host firewall (Windows)


New-NetFirewallRule -DisplayName "Block-CVE-2026-3255" -Direction Inbound -Action Block -Protocol TCP -LocalPort 80,443 -RemoteAddress Any -Enabled True
Get-NetFirewallRule -DisplayName "Block-CVE-2026-3255"

Disable the affected service (Linux)


sudo systemctl stop http-session2 2>/dev/null || true
sudo systemctl disable http-session2 2>/dev/null || true

If the vendor advisory lists an official workaround, prefer that wording verbatim. If no workaround is published, the only safe remediation is the patch.

How to verify the fix worked

After upgrading, confirm the installed version matches the patched build and that no old library is still loaded by a long-running process.


# Linux
dpkg -s http-session2 2>/dev/null | grep -i ^Version
rpm -q http-session2 2>/dev/null || true
# Pid map check for old library handles
sudo lsof +c0 2>/dev/null | grep -i "DEL.*lib" || true


# Windows
Get-Package -Name "*HTTP::Session2*" | Select-Object Name, Version
Get-HotFix | Sort-Object InstalledOn -Descending | Select-Object -First 5

Expected: the reported version is at or above See vendor advisory. Restart the affected service (systemctl restart <service> on Linux, or restart the Windows service) so it loads the patched binary.

Frequently asked questions

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

How to Fix CVE-2026-1881: Insecure Direct Object Reference in Broadstreet — Insecure Direct Object Reference in Broadstreet
How to Fix CVE-2026-6874: Reliance on Reverse DNS Resolution in copilot-api — Reliance on Reverse DNS Resolution in copilot-api
How to Fix CVE-2026-42311: Integer Overflow or Wraparound in Pillow , Integer Overflow or Wraparound in Pillow
How to Fix CVE-2026-23878: Critical Vulnerability in hotcrp , Critical Vulnerability in hotcrp
How to Fix CVE-2026-34753: vLLM affected by Server-Side Request Forgery (SSRF) in download_bytes_from_url , vLLM affected by Server-Side Request Forgery (SSRF) in download_bytes_from_url

Is CVE-2026-3255 actively exploited?

There is no public confirmation of exploitation in the wild listed in CISA KEV at the time of this writing. Patch anyway. Public exploits commonly follow disclosure within weeks.

Do I need to reboot after patching CVE-2026-3255?

For kernel and OS-level updates, yes. For most userland packages a systemctl restart <service> is enough on Linux, and restarting the Windows service or app on Windows. Any process that loaded the old library keeps using it until restarted.

What is the CVSS score for CVE-2026-3255?

6.5 (Medium). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:L.

Where is the official advisory for CVE-2026-3255?

The vendor advisory is at https://metacpan.org/release/TOKUHIROM/HTTP-Session2-1.11/source/lib/HTTP/Session2/Random.pm#L35. The NVD record is at https://nvd.nist.gov/vuln/detail/CVE-2026-3255.

References

Official vendor advisory: https://metacpan.org/release/TOKUHIROM/HTTP-Session2-1.11/source/lib/HTTP/Session2/Random.pm#L35
NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-3255
CISA KEV catalog: https://www.cisa.gov/known-exploited-vulnerabilities-catalog
Additional reference: https://metacpan.org/release/TOKUHIROM/HTTP-Session2-1.01/source/lib/HTTP/Session2/ServerStore.pm#L68
Additional reference: https://metacpan.org/release/TOKUHIROM/HTTP-Session2-1.12/changes
Additional reference: https://github.com/tokuhirom/HTTP-Session2/commit/9cfde4d7e0965172aef5dcfa3b03bb48df93e636.patch

*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.*