What is the CVSS score of CVE-2026-34578?

CVE-2026-34578 has a CVSS 3.1 base score of 8.2 (High). CVSS vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:L/A:N. EPSS exploitation probability: 0.2%.

How to fix or mitigate CVE-2026-34578?

Within 24 hours: Identify all OPNsense appliances in your environment and determine current version numbers; isolate WebGUI access to trusted administrative networks via network-level controls. Within 7 days: Upgrade all affected OPNsense instances to version 26.1.6 or later; verify LDAP configuration post-upgrade. Within 30 days: Audit LDAP group membership and administrative access; review authentication logs for suspicious login patterns or username enumeration attempts.

Opnsense CVE-2026-34578

Q: Which versions of Opnsense are affected by CVE-2026-34578?

OPNsense firewalls prior to version 26.1.6 contain an LDAP filter injection vulnerability in the WebGUI login page that enables unauthenticated attackers to enumerate valid usernames and bypass…. A patch is available.

EUVD-2026-20896 HIGH

LDAP Injection (CWE-90)

2026-04-09 GitHub_M

Authentication Bypass LDAP Code Injection Opnsense Core

8.2

CVSS 3.1 · Vendor: GitHub_M

View

Attack ChainAIDerived

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

Access

Access OPNsense WebGUI login page
Exploit

Inject LDAP filter metacharacters into username field
Execution

Bypass LDAP group membership restrictions
Impact

Authenticate as arbitrary LDAP user

Vulnerability Assessment

Weakness	CWE CWE-90 OWASP Top 10:2025 A05:2025 - Injection ASVS 5.0 V1 - Encoding and Sanitization LDAP query parameterization MITRE ATT&CK 1 technique across 1 tactic: Initial Access The technique list with ATT&CK links and the kill-chain view is part of the Basic plan and up. Sign in to read
Exploitation Conditions	OPNsense versions prior to 26.1.6 with LDAP authentication enabled in WebGUI. Remote unauthenticated attacker exploits unescaped username field in LDAP search filter. No victim interaction required. Group membership restriction bypass only when Extended Query is configured.
Impact	CVSS 8.2 reflects high impact: unauthenticated network attacker can enumerate LDAP users and bypass group-based access controls via filter injection. Network-exposed OPNsense instances running vulnerable LDAP authentication face direct compromise risk if attacker knows target credentials. Severity tempered by requirement for pre-existing valid passwords to achieve full authentication bypass.
Exploit ScenarioDerived	Attacker submits crafted LDAP filter syntax in WebGUI login username field (e.g., `)(uid=` to enumerate users or bypass group filters). No authentication required; low complexity injection. Known vulnerable versions prior to 26.1.6; no KEV confirmation or public POC identified at time of analysis.

This Week Schedule remediation this week. Why: HIGH severity (CVSS 7.0-8.9).

Patch available 0.2% exploitation probability (EPSS)

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AnalysisAIv1 – Apr 09, 2026

LDAP filter injection in OPNsense firewall allows unauthenticated attackers to enumerate valid LDAP usernames and bypass group membership restrictions via the WebGUI login page. Affects OPNsense versions prior to 26.1.6. The vulnerability stems from failure to escape user-supplied input before insertion into LDAP search filters, enabling metacharacter injection. Attackers can authenticate as any LDAP user with known credentials, circumventing Extended Query group membership controls. No public exploit identified at time of analysis.

RemediationAI

Vendor-released patch: OPNsense 26.1.6. Upgrade immediately to patched version via WebGUI (System > Firmware > Updates) or command line using opnsense-update utility. Upstream fix implements proper input sanitization through ldap_escape() function (commit 016f66cb4620cd48183fa97843f343bb71813c6e). Organizations unable to upgrade immediately should disable LDAP authentication and switch to local authentication or alternative authentication backends until patching is completed. No effective workaround exists while LDAP authentication remains enabled. Review authentication logs for suspicious username patterns containing LDAP metacharacters (parentheses, asterisks, ampersands). Advisory: https://github.com/opnsense/core/security/advisories/GHSA-jpm7-f59c-mp54

Affected VersionsENISA

core < 26.1.6

Affected Packages

euvd core fix: 26.1.6

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

Root cause is missing ldap_escape() call on username input (CWE-90: Improper Neutralization of Special Elements). LDAP filter metacharacters injected through username field manipulate search filter logic, allowing filter manipulation attacks. When Extended Query group restrictions are configured, injected filters can OR arbitrary conditions to bypass membership checks in authentication logic.

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Exploit and PoC references, threat intelligence from 22 sources

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Severity by source

Vendor (GitHub_M) PRIMARY 8.2 HIGH

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

Primary rating from Vendor (GitHub_M) · only source for this CVE.

CVSS VectorVendor: GitHub_M

Attack Vector

Network

Attack Complexity

Low

Privileges Required

None

User Interaction

None

Scope

Unchanged

Confidentiality

High

Integrity

Low

Availability

None

Lifecycle Timeline

Analysis Updated

Apr 16, 2026 - 06:00 EUVD-patch-fix

executive summary

Patch available

Apr 16, 2026 - 05:29 EUVD

26.1.6

CVE Published

Apr 09, 2026 - 14:34 nvd

HIGH 8.2

DescriptionCVE.org

OPNsense is a FreeBSD based firewall and routing platform. Prior to 26.1.6, OPNsense's LDAP authentication connector passes the login username directly into an LDAP search filter without calling ldap_escape(). An unauthenticated attacker can inject LDAP filter metacharacters into the username field of the WebGUI login page to enumerate valid LDAP usernames in the configured directory. When the LDAP server configuration includes an Extended Query to restrict login to members of a specific group, the same injection can be used to bypass that group membership restriction and authenticate as any LDAP user whose password is known, regardless of group membership. This vulnerability is fixed in 26.1.6.

Executive ViewAI

Why It Matters

OPNsense firewalls prior to version 26.1.6 contain an LDAP filter injection vulnerability in the WebGUI login page that enables unauthenticated attackers to enumerate valid usernames and bypass group-based access controls, potentially allowing unauthorized administrative access to network perimeter security infrastructure. Organizations using OPNsense with LDAP authentication face immediate risk of credential compromise and loss of authentication-based access restrictions that protect critical network management functions.

Business Impact: High

Compensating Controls

Apply vendor patch (OPNsense 26.1.6 or later). Interim mitigations: restrict WebGUI access to specific source IPs via firewall rules or network segmentation; implement rate limiting on login endpoints; enforce multi-factor authentication for administrative accounts; monitor LDAP query logs for suspicious search patterns.

Threat Intelligence Overview

EPSS Score

0.2%

Top 58% exploitable

Data Quality

6 sources

Confidence: High

EUVD

NVD

CVE.org

EPSS

Vulnrichment

GitHub

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 HIGH

CISA KEV No

Public POC No

EPSS 0.2%

Patch available Yes

Active threat No

Deciding rule

HIGH severity (CVSS 7.0-8.9)

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

Out-of-Cycle

Exploitation

Poc

System Exposure· derived

Open

Automatable

Yes

Human Impact

High

Technical Impact

Partial

Priority Score

Low Medium High Critical

KEV: 0

EPSS: 0

CVSS: +41

PoC: 0

Weaponized: 0

Threat intel: 0

Gov advisory: 0

Attack Technique

Authentication Bypass CRITICAL

Authentication bypass attacks exploit flaws in the verification mechanisms that control access to systems and applications.

Code Injection CRITICAL

Code injection occurs when an application accepts user input and passes it directly into a language interpreter or evaluator without proper sanitization.