What is the CVSS score of CVE-2026-3256?

CVE-2026-3256 has a CVSS 3.1 base score of 9.8 (Critical). CVSS vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H. EPSS exploitation probability: 0.0%.

Http CVE-2026-3256

EUVD-2026-16939 CRITICAL

Generation of Predictable Numbers or Identifiers (CWE-340)

2026-03-28 CPANSec

GHSA-mx9c-4xjq-mhj6

Information Disclosure Http

9.8

CVSS 3.1 · NVD

View

Attack ChainAIDerived

Hypothetical attack flow derived from CVE metadata – not a confirmed exploit chain

Access

Capture HTTP Date header from server response
Exploit

Predict session ID using weak rand seed and PID
Execution

Forge valid session cookie
Impact

Hijack user session with full access

Vulnerability Assessment

Weakness	CWE CWE-340
Exploitation Conditions	HTTP::Session Perl module versions through 0.53 using default SHA-1 session ID generation. Remote unauthenticated attacker can predict session IDs by guessing PID (small set), epoch time (from HTTP Date header or inference), and weak rand seeding. No victim interaction required.
Exploit ScenarioDerived	Attacker intercepts HTTP responses to obtain server epoch time, then uses predictable rand() seeding combined with common PIDs to brute-force valid HTTP::Session IDs. With a forged session cookie, the attacker gains unauthorized access to authenticated user sessions without credentials.

Act Now Prioritize within 24-48h. Why: CRITICAL severity.

No patch listed yet 0.0% exploitation probability (EPSS)

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AnalysisAIv1 – Mar 28, 2026

HTTP::Session versions through 0.53 for Perl defaults to using insecurely generated session ids.

Earlier versions of this analysis (1)

v1 Mar 28, 2026 - 19:15 CVSS 9.8

RemediationAI

Monitor vendor advisories for patches. Apply mitigations such as network segmentation, access restrictions, and monitoring.

Affected VersionsENISA

HTTP::Session 0 ≤0.53

Affected Packages

euvd http_session no fix

Source: OSV (Open Source Vulnerabilities)

Affects your stack

Affects 1 package in euvd

Checking this CVE against your own stacks and servers is part of the Basic plan and up.

Technical ContextAI · show details

This vulnerability is classified as Generation of Predictable Numbers or Identifiers (CWE-340).

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Exploit and PoC references, threat intelligence from 22 sources

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Severity by source

NVD PRIMARY 9.8 CRITICAL

AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Primary rating from NVD · only source for this CVE.

CVSS VectorNVD

Attack Vector

Network

Attack Complexity

Low

Privileges Required

None

User Interaction

None

Scope

Unchanged

Confidentiality

High

Integrity

High

Availability

High

DescriptionNVD

HTTP::Session versions through 0.53 for Perl defaults to using insecurely generated session ids.

HTTP::Session defaults to using HTTP::Session::ID::SHA1 to generate session ids using a SHA-1 hash seeded with the built-in rand function, the high resolution 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.

The distribution includes HTTP::session::ID::MD5 which contains a similar flaw, but uses the MD5 hash instead.

Threat Intelligence Overview

EPSS Score

0.0%

Top 100% exploitable

Data Quality

6 sources

Confidence: High

EUVD

NVD

CVE.org

EPSS

Vulnrichment

VulDB

How this decision was reached

The engine reads each signal below and applies a fixed list of rules from top to bottom. The first rule that matches sets the recommended action – like a statement, every line is shown.

SignalValue

Severity CRITICAL

CISA KEV No

Public POC No

EPSS 0.0%

Patch available No

Active threat No

Deciding rule

CRITICAL severity

What every action level means

Emergency Immediate action required. Criteria: CRITICAL + in CISA KEV (actively exploited) without patch, OR CRITICAL + EPSS > 30% without patch, OR CRITICAL + active threat signals without patch.

Act Now Prioritize within 24-48h. Criteria: in KEV with patch available, OR CRITICAL + public POC, OR HIGH + EPSS > 10%, OR CRITICAL + active threat, OR any CRITICAL severity.

This Week Schedule remediation this week. Criteria: HIGH severity (CVSS 7.0-8.9). Patch within normal change window.

This Month Plan within 30 days. Criteria: MEDIUM severity (CVSS 4.0-6.9), lower exploitation probability. Include in regular patch cycle.

Monitor Track and reassess. Criteria: LOW severity (CVSS 0.1-3.9), minimal exploitation risk. No immediate action needed.

SSVC AssessmentENISA

SSVC Decision· derived

Scheduled

Exploitation

None

System Exposure· derived

Open

Automatable

Yes

Human Impact· derived

Medium

Technical Impact

Total

Priority Score

Low Medium High Critical

KEV: 0

EPSS: 0

CVSS: +49

PoC: 0

Weaponized: 0

Threat intel: 0

Gov advisory: 0

Attack Technique

Information Disclosure MEDIUM

Information disclosure occurs when an application unintentionally exposes sensitive data that aids attackers in reconnaissance or directly compromises security.