How severe is CVE-2016-4437?

CVE-2016-4437 has a CVSS score of 9.8/10, rated CRITICAL. Immediate patching is strongly recommended.

Which packages are affected by CVE-2016-4437?

CVE-2016-4437 affects the following packages: org.apache.shiro:shiro-core (Maven). Ecosystems affected: Maven.

How do I fix CVE-2016-4437?

Update org.apache.shiro:shiro-core to 1.2.5 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2016-4437 is resolved across your whole dependency graph.

How do I detect CVE-2016-4437 in my Maven dependencies?

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

How do I mitigate CVE-2016-4437 if there is no patch (or I can't update yet)?

If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.

Is CVE-2016-4437 actively exploited in the wild?

Yes. There are 10 known exploit references for CVE-2016-4437, including 1 documented proof-of-concept exploit on Exploit-DB and 6 in-the-wild exploitations observed on GitHub and other sources. Treat this as actively exploitable and prioritize patching immediately. All exploit code should only be run in an isolated sandbox environment for research or authorized testing — never against production systems without explicit written authorization.

What is the EPSS score for CVE-2016-4437?

CVE-2016-4437 has an EPSS (Exploit Prediction Scoring System) score of 93.0%, placing it in the 100th 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. A score above 50% indicates significantly elevated exploitation risk — immediate patching is strongly recommended.

Is CVE-2016-4437 in the CISA Known Exploited Vulnerabilities catalog?

Yes. CVE-2016-4437 (Apache Shiro Code Execution Vulnerability) was added to CISA's Known Exploited Vulnerabilities (KEV) catalog on 2021-11-03. CISA required all US federal civilian agencies to remediate this vulnerability by 2022-05-03. The required action was: Apply updates per vendor instructions. Being listed in the KEV catalog is the strongest possible confirmation of active exploitation — treat this as a critical priority.

What type of vulnerability is CVE-2016-4437?

CVE-2016-4437 is classified as CWE-321 (CWE-321). This weakness type describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation.

Is there exploit tooling available for CVE-2016-4437?

A Nuclei detection template exists for CVE-2016-4437, meaning automated scanners can fingerprint it. Public exploit tooling significantly increases real-world risk — prioritize patching and ensure detection coverage. Exploit tooling should only ever be used in isolated, authorized testing environments.

When was CVE-2016-4437 published, and has it been updated?

CVE-2016-4437 was published on June 7, 2016 and was last updated on October 20, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

☕

☕ Maven

CISA KEV · ACTIVELY EXPLOITED

CRITICAL severity

CVE-2016-4437 — shiro-core

CRITICAL

CVE-2016-4437 is a critical-severity (CVSS 9.8) CWE-321 vulnerability in org.apache.shiro:shiro-core. It is in CISA's Known Exploited Vulnerabilities catalog (added 2021-11-03) — treat it as actively exploited and patch now. A fix is available for org.apache.shiro:shiro-core — see the affected versions and patch details below.

Improper Access Control in Apache Shiro

Also known asGHSA-p836-389h-j692

Published

Jun 7, 2016

Updated

Oct 20, 2026

Affected

1 pkg

Patched

1 / 1

Exploits

10 known

Exploitation data as of Oct 22, 2026 · OSV.dev, NVD, CISA KEV, FIRST.org (EPSS)

Exploitation Status

Actively exploited in the wild

Confirmed by CISA's Known Exploited Vulnerabilities catalog on 2021-11-03. Federal agencies were required to remediate by 2022-05-03.
CISA assesses this as automatable — exploitation doesn’t require manual, per-target effort, which raises the odds of mass scanning and opportunistic attacks.
A successful exploit gives an attacker total control of the affected component, not partial access.

Exploitation and automatability from CISA (KEV catalog and SSVC triage) for CVE-2016-4437.

EPSS Exploitation Probability

via FIRST.org ↗

93.0%probability of exploitation in next 30 days

Very High Risk0.00%

Lower risk than most CVEs100th percentile — riskier than 100% of all scored CVEsHighest risk

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

How urgent is this, really

CVE-2016-4437 by exploitation likelihood (EPSS) against impact (CVSS). In the shaded patch-first corner (EPSS 50%+, CVSS 7.0+).

Where this sits among everything scored

Of 394,803 CVEs with a current EPSS score, this one falls in the ≥ 90% band (highlighted). Counts from FIRST.org, log-scaled.

Real-World Exposure

1 pkg affected

☕org.apache.shiro:shiro-core

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

Description

Apache Shiro before 1.2.5, when a cipher key has not been configured for the "remember me" feature, allows remote attackers to execute arbitrary code or bypass intended access restrictions via an unspecified request parameter.

Affected Packages

1 total 1 fixed

Ecosystem	Package	Vulnerable range	Fix
☕Maven	`org.apache.shiro:shiro-core`	all versions	1.2.5`org.apache.shiro:shiro-core:1.2.5`

Affected Products

4 products · 4 configurations

Application

auroraapache

≥ 0.10.0 && < 0.18.1

range

Application

shiroapache

< 1.2.5

range

Application

fuseredhat

1 version

1.0

Application

jboss middleware text-only advisoriesredhat

1 version

1.0

Exploits & PoCs

Research use only. For defensive security, authorized penetration testing, and academic research only. Never execute exploit code against systems without explicit written authorization.

EDB-48410remotemultiple✓ Verified

Apache Shiro 1.2.4 - Cookie RememberME Deserial RCE (Metasploit)

by Metasploit · May 1, 2020

Exploit-DB Source

Detection & mitigation playbook

Open-source dependency

Detect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for org.apache.shiro:shiro-core, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update org.apache.shiro:shiro-core to 1.2.5 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2016-4437 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.

How to detect CVE-2016-4437

A community-maintained Nuclei template exists for this CVE. You can scan for it directly:

nuclei -id cve-2016-4437 -u https://target

Template: Apache Shiro 1.2.4 Cookie RememberME - Deserial Remote Code Execution Vulnerability
Severity: high
Impact: Remote code execution
Remediation: Upgrade to a patched version of Apache Shiro

Template by ProjectDiscovery nuclei-templates (iamnoooob, rootxharsh, pdresearch), MIT licensed. View the full template. Scan only systems you are authorised to test.

Fixing This On Your OS

If you run this on a Linux distribution, patch through your package manager against the distro's own security advisory below — it tracks the exact backported fix for your release, which can ship on a different timeline (and sometimes a different severity) than the upstream project.

Red HatImportant

RHSA-2016:2036Red Hat JBoss A-MQ 6.3 RHSA-2016:2035Red Hat JBoss Fuse 6.3

UbuntuCRITICAL

USN-7139-1Ubuntu

Frequently Asked Questions

O3 Security · Impact-Aware SCA

Is CVE-2016-4437 in your dependencies?

Find it across Maven, 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:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

CWE Classification

Weaponization

Timeline

Disclosed

Jun 7, 2016

First exploit

May 1, 2020

KEV added

Nov 3, 2021

Last updated

Oct 20, 2026

Identifiers

CVE-2016-4437

GHSA-p836-389h-j692

References

Advisorypacketstormsecurity.com Advisoryrhn.redhat.com Advisoryrhn.redhat.com Advisorysecurityfocus.com Advisorysecurityfocus.com Advisorynvd.nist.gov Articlelists.apache.org Webcisa.gov Weblists.apache.org Evidencepacketstormsecurity.com

Related vulnerabilities

This CVE is critical severity; 4 of 8 other CVEs affecting shiro-core are rated as high or higher (top: critical).

CVE-2026-49268CVE-2026-43827CVE-2026-23901CVE-2023-46749CVE-2022-40664CVE-2022-32532CVE-2021-41303CVE-2020-1957

Provenance

Sources

OSV.devNVDCISA KEVFIRST.org (EPSS)

Last verifiedOct 20, 2026

CVE-2016-4437 — shiro-core

Exploitation Status

Actively exploited in the wild

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

How to detect CVE-2016-4437

Fixing This On Your OS

Frequently Asked Questions

Is CVE-2016-4437 in your dependencies?