How severe is CVE-2016-2403?

CVE-2016-2403 has a CVSS score of 9.8/10, rated CRITICAL. Immediate patching is strongly recommended.

Which packages are affected by CVE-2016-2403?

CVE-2016-2403 affects the following packages: symfony/security-core (Packagist), symfony/security-core (Packagist), symfony/security (Packagist), symfony/security (Packagist), symfony/symfony (Packagist), symfony/symfony (Packagist). Ecosystems affected: Packagist.

How do I fix CVE-2016-2403?

Update symfony/security-core to 2.8.6 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2016-2403 is resolved across your whole dependency graph.

How do I detect CVE-2016-2403 in my Packagist dependencies?

Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for symfony/security-core, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

How do I mitigate CVE-2016-2403 if there is no patch (or I can't update yet)?

Put an independent control in front of the weakness: restrict the affected endpoint or interface to trusted networks, require an additional authentication factor or proxy-level check, and invalidate existing sessions and credentials in case the flaw has already been used.

Is CVE-2016-2403 actively exploited in the wild?

No public exploit code has been indexed for CVE-2016-2403 yet. This does not mean the vulnerability cannot be exploited — absence of public exploits does not imply safety. Apply the recommended fix and use O3 Security to monitor your exposure.

What is the EPSS score for CVE-2016-2403?

CVE-2016-2403 has an EPSS (Exploit Prediction Scoring System) score of 4.3%, placing it in the 91th percentile of all CVEs. EPSS is maintained by FIRST.org and estimates the probability that a vulnerability will be exploited in the wild within the next 30 days. This score indicates relatively lower exploitation probability, though the CVSS severity should still guide your patching priority.

What type of vulnerability is CVE-2016-2403?

CVE-2016-2403 is classified as Improper Authentication (CWE-287). This weakness type describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation.

When was CVE-2016-2403 published, and has it been updated?

CVE-2016-2403 was published on February 7, 2017 and was last updated on October 24, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

🐘

🐘 Packagist

Not in CISA KEV

CRITICAL severity

CVE-2016-2403 — security-core

CRITICAL

CVE-2016-2403 is a critical-severity (CVSS 9.8) Improper Authentication vulnerability in symfony/security-core. A fix is available for symfony/security-core — see the affected versions and patch details below.

Symfony Authentication Bypass

Also known asGHSA-wvj5-r78r-hhfq

Published

Feb 7, 2017

Updated

Oct 24, 2026

Affected

6 pkgs

Patched

6 / 6

Exploits

None indexed

Exploitation data as of Nov 4, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

EPSS Exploitation Probability

via FIRST.org ↗

4.3%probability of exploitation in next 30 days

Lower Risk0.00%

Lower risk than most CVEs91th percentile — riskier than 91% of all scored CVEsHighest risk

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

How urgent is this, really

Where this sits among everything scored

Real-World Exposure

6 pkgs affected

🐘symfony/security-core🐘symfony/security-core🐘symfony/security🐘symfony/security🐘symfony/symfony🐘symfony/symfony

Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects Packagist packages — download data is not available via public APIs for these ecosystems.

Description

Symfony before 2.8.6 and 3.x before 3.0.6 allows remote attackers to bypass authentication by logging in with an empty password and valid username, which triggers an unauthenticated bind.

Affected Packages

6 total 6 fixed

Ecosystem	Package	Vulnerable range	Fix
🐘Packagist	`symfony/security-core`	≥ 2.8.0&&< 2.8.6	2.8.6`composer require symfony/security-core:^2.8.6`
🐘Packagist	`symfony/security-core`	≥ 3.0.0&&< 3.0.6	3.0.6`composer require symfony/security-core:^3.0.6`
🐘Packagist	`symfony/security`	≥ 2.8.0&&< 2.8.6	2.8.6`composer require symfony/security:^2.8.6`
🐘Packagist	`symfony/security`	≥ 3.0.0&&< 3.0.6	3.0.6`composer require symfony/security:^3.0.6`
🐘Packagist	`symfony/symfony`	≥ 2.8.0&&< 2.8.6	2.8.6`composer require symfony/symfony:^2.8.6`
🐘Packagist	`symfony/symfony`	≥ 3.0.0&&< 3.0.6	3.0.6`composer require symfony/symfony:^3.0.6`

Affected Products

1 product · 12 configurations

Application

symfonysensiolabs

12 versions

2.8.02.8.12.8.22.8.32.8.42.8.53.0.03.0.13.0.23.0.33.0.43.0.5

Detection & mitigation playbook

Open-source dependency

Detect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for symfony/security-core, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update symfony/security-core to 2.8.6 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2016-2403 is resolved across your whole dependency graph.
Workarounds
Put an independent control in front of the weakness: restrict the affected endpoint or interface to trusted networks, require an additional authentication factor or proxy-level check, and invalidate existing sessions and credentials in case the flaw has already been used.

Frequently Asked Questions

Symfony before 2.8.6 and 3.x before 3.0.6 allows remote attackers to bypass authentication by logging in with an empty password and valid username, which triggers an unauthenticated bind.

O3 Security · Impact-Aware SCA

Is CVE-2016-2403 in your dependencies?

Find it across Packagist, including transitive dependencies.

Scan my dependencies How O3 SCA works

CVSS Score

9.8/10CVSS v3 base

Vector breakdown

Attack Vector

Network

Attack Complexity

Low

Privileges Required

None

User Interaction

None

Scope

Unchanged

Confidentiality

High

Integrity

High

Availability

High

Raw vector

CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

CWE Classification

CWE-287Improper Authentication

Weaponization

No Nuclei template, Metasploit module or public proof-of-concept found.

OpenSSF Scorecard

Package health score

security-advisories

4.8/10

Maintained10/10

Code-Review10/10

Branch-Protection0/10

Assessed Nov 2, 2026

Timeline

Disclosed

Feb 7, 2017

Last updated

Oct 24, 2026

Identifiers

CVE-2016-2403

GHSA-wvj5-r78r-hhfq

References

Advisorysymfony.com · cve 2016 2403 unauthorized access on a misconfigured ldap server when using an empty password Advisorysecurityfocus.com Advisorydebian.org · dsa 4262 Advisorynvd.nist.gov · CVE 2016 2403 Webgithub.com · CVE 2016 2403.yaml Webgithub.com · CVE 2016 2403.yaml Webgithub.com · CVE 2016 2403.yaml Websymfony.com · cve 2016 2403 Webweb.archive.org

Related vulnerabilities

Also affects symfony/security-core

This CVE is critical severity; 2 of 4 other CVEs affecting symfony/security-core are rated as high or higher (top: critical).

CVE-2017-11365CVE-2016-1902CVE-2018-11407CVE-2021-21424

Also affects symfony/security

This CVE is critical severity — higher than any of the other 4 CVEs affecting symfony/security (highest there: high).

CVE-2012-6431CVE-2013-5958CVE-2015-8125CVE-2016-4423

Provenance

Sources

OSV.devNVDFIRST.org (EPSS)

Last verifiedOct 24, 2026

CVE-2016-2403 — security-core

EPSS Exploitation Probability

How urgent is this, really

Where this sits among everything scored

Real-World Exposure

Description

Affected Packages

Affected Products

Detection & mitigation playbook

Detect

Fix

Workarounds

Frequently Asked Questions

Is CVE-2016-2403 in your dependencies?