CriticalCVE-2016-4437

    Apache Shiro Code Execution Vulnerability (CVE-2016-4437)

    Published In CISA KEV since Sources: CVE.org, OSV

    What is affected, what to do

    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.

    The vulnerability is being actively exploited; treat it as a priority. Update Apache Aurora to version 0.18.1, Apache Shiro to version 1.2.5. Immediate actions, mitigation and detection rules are in the runbook below.

    Affected
    • Apache Aurora lt 0.10.0..0.18.1
    • Apache Shiro lt *..1.2.5
    • Red Hat Fuse 7 eq 1.0..1.0
    • Red Hat Jboss Middleware Text-only Advisories eq 1.0..1.0
    Fixed in
    • Apache Aurora 0.18.1
    • Apache Shiro 1.2.5

    Not sure whether and how you are affected? Ask a question about this vulnerability

    Metrics

    9.8

    Priority

    XIEM Effective CVSS: highest available CVSS rating from NVD and vendor data.

    Source: NVD, CVSS v3

    9.8

    CVSS v3

    Severity Critical on the scale from 0 to 10.

    Source: CVE.org, OSV

    93.0 %

    EPSS score

    High — model estimates ≥ 50% chance of real-world exploitation within 30 days.

    Source: FIRST EPSS, percentile 99.83

    Show all metrics
    Severity
    Critical
    Priority (0–325)

    The priority score is a consolidated metric that condenses several individual signals into a single, action-guiding ranking: technical severity (CVSS), exploitation likelihood (EPSS), known-exploited status (KEV) and the context of the affected asset. The aim is to answer the only truly important question in vulnerability management: what first?

    Read in glossary
    228.73 Methodology
    Exploit maturity

    An exploit is code or a technique that specifically uses a concrete vulnerability to force unintended behaviour — such as executing code or escalating privileges. It is the tool that turns a theoretical flaw into a practical attack.

    Read in glossary
    actively exploited
    XIEM Effective CVSS

    XIEM® is the tiered managed-security operating model from NEOSEC and a registered trademark of NEOSEC GmbH. It extends classic SIEM — the central collection, normalisation and correlation of security-relevant events — with endpoint forensics, network visibility and deception technology, and consolidates them into three building tiers: Sentry, Orchestrate and Command.

    Read in glossary
    9.8 Methodology
    CVSS v3

    CVSS is the globally established, open standard for assessing the technical severity of a vulnerability on a scale from 0 to 10. It describes how easily a flaw can be exploited and what damage it can cause — but not how likely its actual exploitation is. CVSS and the complementary EPSS deliberately answer different questions.

    Read in glossary
    9.8
    EPSS score

    The EPSS score is the absolute model output for an individual vulnerability: the estimated probability of real-world exploitation within the next 30 days, expressed as a value between 0 and 1 (i.e. 0 % to 100 %). A score of 0.42 means „the model estimates a 42 % chance of real-world exploitation within 30 days“.

    Read in glossary
    93.0 %
    High — model estimates ≥ 50% chance of real-world exploitation within 30 days.
    EPSS percentile

    The EPSS percentile is the relative position of a vulnerability within all EPSS-scored CVEs, expressed as a value between 0 and 1. A percentile of 0.90 means „this CVE has a higher EPSS score than 90 % of all other scored CVEs“. Unlike the EPSS score, it is not a probability — but a positioning within a ranking.

    Read in glossary
    99.83
    Critical — this CVE ranks in the top fifth of all CVEs scored today (rank ≥ 80%).
    KEV status

    The KEV catalogue is a list maintained by the US authority CISA of vulnerabilities for which active exploitation in the wild has been confirmed. It answers not the question „how severe?“ but „is it already being attacked?“ — thereby sharply prioritising patching.

    Read in glossary
    Actively exploited
    Published
    In CISA KEV since

    The KEV catalogue is a list maintained by the US authority CISA of vulnerabilities for which active exploitation in the wild has been confirmed. It answers not the question „how severe?“ but „is it already being attacked?“ — thereby sharply prioritising patching.

    Read in glossary

    Response and mitigation

    Why act now?

    Prioritisation rationale

    This CVE sits on CISA KEV because it yields unauthenticated remote code execution through a crafted rememberMe cookie whenever the cipher key is left at its public default — no credentials, no user interaction, exploitable against any internet-exposed Shiro login page. Public exploit tooling (notably shiro_exploit.py) has been circulating for years and is actively used by opportunistic mass-scanners; the probability of exploitation is among the highest tracked on the KEV list. Treat any internet-reachable Java web application with a Shiro dependency as P1, internal instances holding sensitive data as P2; embedded Shiro inside legacy products (Aurora, Fuse, JBoss middleware) is the usual blind spot and should be actively hunted via SBOM/SCA rather than trusted to be absent.

    1. Runbook step 1

      Immediate response (0-24 h)

      • Upgrade Apache Shiro to 1.2.5 or later (Apache Aurora: upgrade to 0.18.1). For every embedded Shiro instance inside Java, JBoss or Fuse deployments, verify the effective JAR version on disk (find / -name "shiro-core-*.jar") rather than trusting the declared Maven dependency.
      • If an immediate patch is not possible, configure a cryptographically strong, random cipher key in shiro.ini or Java configuration: securityManager.rememberMeManager.cipherKey = <base64-encoded 128-bit AES key>. The default key is public and is the root cause of the exploit chain.
      • Temporarily disable the RememberMe feature in sensitive applications: set securityManager.rememberMeManager.cookie.maxAge = 0 or remove rememberMeManager from the configuration until patch and new key are rolled out.
      • Invalidate all outstanding RememberMe cookies and active sessions; rotate service-account and API credentials reachable from any potentially compromised Shiro host.
      • Inventory internet-facing Shiro endpoints (reverse-proxy logs for /login.jsp, /j_security_check, admin consoles) and place them behind VPN or IP allowlist for the duration of the patch window.

    2. Runbook step 2

      Mitigation layers

      • WAF / reverse-proxy rule: inspect inbound cookies named rememberMe for abnormal length (>500 bytes) and base64 padding; block or sandbox suspicious payloads. ModSecurity example: SecRule REQUEST_COOKIES:rememberMe "@gt 500" "id:1004437,phase:1,deny,log".
      • Network segmentation: Shiro-hosting application servers should not initiate arbitrary outbound internet traffic. Enforce an egress allowlist to known backend targets (LDAP, DB) and drop the rest to break reverse-shell callbacks from deserialised payloads.
      • JVM hardening: run with -Djava.security.manager and a restrictive java.policy; where feasible, configure SerialKiller or an ObjectInputFilter (JEP 290, Java 8u121+) that blocks org.apache.commons.collections.*, org.apache.commons.beanutils.*, org.codehaus.groovy.runtime.*. These are the gadget chains typically used once the cipher is decrypted.
      • Endpoint hardening: on application servers, block or at minimum alert on java spawning child processes such as sh, bash, cmd.exe, powershell.exe, wget, curl, nc via EDR policy.
      • Transitive dependency monitoring: run an SCA tool (OWASP Dependency-Check, Snyk, Trivy) in CI, because Shiro is frequently pulled in transitively by legacy frameworks and escapes manual inventories.

    3. Runbook step 3

      Detection rules

      • Zeek/Suricata or web access log: HTTP requests carrying Cookie: rememberMe= with cookie length over 300 bytes, correlated with HTTP 500 responses or anomalous response time. Sigma shape: selection: cs-cookie|contains: "rememberMe=" AND cs-cookie|re: ".{300,}".
      • Sysmon EID 1 / Linux auditd execve: java as parent of a shell or download utility (sh, bash, powershell.exe, cmd.exe, curl, wget, certutil). KQL: DeviceProcessEvents | where InitiatingProcessFileName == "java.exe" and FileName in ("cmd.exe","powershell.exe","bitsadmin.exe").
      • Application log: repeated DecryptionException, InvalidCipherTextException or UnknownAccountException from org.apache.shiro.crypto.* within short time windows indicates cipher-key brute-forcing.
      • Network telemetry: outbound connections from the app-server host to unlisted IPs on ports 4444, 1337, 8080, 443 immediately following a login request bearing a large rememberMe cookie.
      • File-integrity monitoring: new .jsp or .class files appearing in webapp deployment directories (webapps/, deployments/), or unexpected changes to shiro.ini.

    Detection rules

    No NEOSEC detection rule is available for this vulnerability yet.

    Classification under NIS2 and CRA

    Rule-based classification from exploitation status and severity. It does not replace a case-by-case assessment.

    NIS2

    NIS2 is EU Directive (EU) 2022/2555 to raise the level of cybersecurity across the Union. It substantially broadens obligations compared with the first NIS directive: more sectors, mandatory risk management, staged reporting duties and personal accountability of senior management.

    Read in glossary
    Actively exploited: treat the vulnerability as a priority in vulnerability handling under Art. 21(2)(e) NIS2. If it is exploited in your environment, check the reporting obligation under Art. 23 (early warning within 24 hours).
    CRA

    The CRA is EU Regulation (EU) 2024/2847 setting horizontal cybersecurity requirements for „products with digital elements“ — from industrial controllers and software to connected consumer devices. For the first time manufacturers must ensure security across the entire product lifecycle, handle vulnerabilities and provide security updates.

    Read in glossary
    Since 11.09.2026, manufacturers of affected products with digital elements must report actively exploited vulnerabilities under Art. 14 CRA, with an early warning within 24 hours via ENISA's single reporting platform.
    ISO/IEC 27001

    ISO/IEC 27001 is the internationally leading standard for an information security management system (ISMS). It describes a risk-based, process-oriented framework to systematically plan, implement, review and improve information security.

    Read in glossary
    Control A.8.8, management of technical vulnerabilities: assess relevance to your systems, plan remediation and keep evidence.

    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.

    Source: NVD (NIST), OSV (Open Source Vulnerabilities), cvelistv5, CISA KEV Catalog, CVE.org (MITRE)

    Affected products

    The following versions are affected. Older releases of the same product line are also vulnerable unless stated otherwise.

    Affected products
    Affected versionsFixed in
    apacheaurora
    • 0.10.0 – < 0.18.1
    • 0.18.1
    apacheshiro
    • < 1.2.5
    • 1.2.5
    redhatfuse
    • 1.0
    • —
    redhatjboss_middleware_text-only_advisories
    • 1.0
    • —
    mavenorg.apache.shiro:shiro-core
    • 1.2.0
    • 1.1.0
    • 1.2.3
    • 1.2.2
    • 1.0.0-incubating
    • 1.2.1
    • 1.2.4
    • —
    • —
    • —
    • —
    • —
    • —
    • —

    Vendors and products

    Public exploit references

    Publicly reported proof-of-concepts, exploit modules and detection templates for this vulnerability. NEOSEC links to the original sources only and does not provide any exploit code.

    Public exploit references
    CISA KEV CatalogCISA Known Exploited Vulnerability (opens in a new tab)cisa.govactively exploited
    Packet StormApache Shiro 1.2.4 Information Disclosure (opens in a new tab)packetstormsecurity.comPoC (publicly reported)reported, not verified—
    Packet StormApache Shiro 1.2.4 Remote Code Execution (opens in a new tab)packetstormsecurity.comPoC (publicly reported)reported, not verified—
    PoC-in-GitHub (nomi-sec)vulhub-shiro-cve-2016-4437 (opens in a new tab)github.comPoC (publicly reported)reported, not verified

    References & sources

    • NVD (NIST)vuln/detail/CVE-2016-4437advisory
    • lists.apache.org[announcements@aurora.apache.org] 20171101 Apache Aurora information disclosure vulnerabilityweb, Mailing list, x_refsource_MLIST, Mailing list
    • lists.apache.orgthread.html/ef3a800c7d727a00e04b78e2f06c5cd8960f09ca28c9b69d94c…web
    • cisa.govknown-exploited-vulnerabilities-catalog?field_cve=CVE-2016-4437web, government-resource, US government resource
    • packetstormsecurity.comfiles/137310/Apache-Shiro-1.2.4-Information-Disclosure.htmlweb, x_refsource_MISC, Third-party advisory, Vulnerability database
    • packetstormsecurity.comfiles/157497/Apache-Shiro-1.2.4-Remote-Code-Execution.htmlweb, x_refsource_MISC, Exploit, Third-party advisory, Vulnerability database
    • rhn.redhat.comRHSA-2016:2035web, Vendor advisory, x_refsource_REDHAT, Third-party advisory
    • rhn.redhat.comRHSA-2016:2036web, Vendor advisory, x_refsource_REDHAT, Third-party advisory
    • securityfocus.com20160603 [Announce] CVE-2016-4437: Apache Shiro information disclosure vulnerabilityweb, Mailing list, x_refsource_BUGTRAQ, Broken link, Third-party advisory, Vulnerability database
    • securityfocus.com91024web, Vulnerability database, x_refsource_BID, Broken link, Third-party advisory, Vulnerability database
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