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PatchSiren cyber security CVE debrief

CVE-2016-2403 Sensiolabs CVE debrief

CVE-2016-2403 is a critical authentication-bypass issue in Symfony. On affected versions, a remote attacker with a valid username could authenticate using an empty password when the application was configured against a misconfigured LDAP server, resulting in an unauthenticated bind and possible full account compromise. NVD rates the issue CVSS 9.8 and maps it to CWE-287.

Vendor
Sensiolabs
Product
Symfony
CVSS
CRITICAL 9.8
CISA KEV
Not listed in stored evidence
Original CVE published
2017-02-07
Original CVE updated
2026-05-13
Advisory published
2017-02-07
Advisory updated
2026-05-13

Who should care

Security, platform, and application teams running Symfony-based applications that use LDAP or directory-backed authentication, especially where login endpoints are exposed to the internet. Debian or other downstream package consumers should also verify whether they inherited the affected Symfony versions.

Technical summary

The vulnerability affects Symfony before 2.8.6 and 3.x before 3.0.6. The trigger described in the advisory is a login attempt using a valid username and an empty password against a misconfigured LDAP server, which can lead to an unauthenticated bind. NVD lists vulnerable Symfony CPEs covering 2.8.0 through 2.8.5 and 3.0.0 through 3.0.5, with CVSS v3.0 9.8 (AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H) and CWE-287.

Defensive priority

Immediate. This is a remote, unauthenticated authentication bypass with critical impact, so upgrading or patching should be treated as a top-priority remediation.

Recommended defensive actions

  • Upgrade Symfony to 2.8.6 or later, or 3.0.6 or later; use a supported maintained release if possible.
  • Review LDAP and authentication configuration for any behavior that could permit empty passwords, anonymous binds, or unintended fallback authentication.
  • Audit login logs and authentication telemetry for successful logins with blank passwords or unusual authentication successes from new IPs or user agents.
  • If exposure is suspected, rotate credentials, invalidate sessions, and review authorization changes performed by potentially bypassed accounts.
  • Apply downstream vendor security updates where applicable, including Debian security guidance referenced for this CVE.

Evidence notes

This debrief is based on the supplied CVE description, the NVD record, and the listed references. The supplied advisory text explicitly states that Symfony before 2.8.6 and 3.x before 3.0.6 can be bypassed via an empty password and valid username on a misconfigured LDAP server. NVD provides the CVSS vector, CWE-287 mapping, and vulnerable version criteria. No KEV entry was provided in the supplied corpus.

Sources and references

Verified primary and authoritative sources

  • CVE-2016-2403 CVE Program record

    Publisher, destination, and source semantics verified

    URL: https://www.cve.org/CVERecord?id=CVE-2016-2403

    CVE Program - Official CVE Program record with source-provided CVE metadata.

  • CVE-2016-2403 NVD vulnerability detail

    Publisher, destination, and source semantics verified

    URL: https://nvd.nist.gov/vuln/detail/CVE-2016-2403

    NIST National Vulnerability Database - Official NIST NVD detail page and source-specific vulnerability assessment.

Supplemental references

Methodology and review provenance

AI-assisted synthesis based on stored public vulnerability evidence. System validation, approval state, and publication status do not by themselves establish human review of this revision. PatchSiren helps prioritize defensive review and does not prove exposure or remediation on any system.