How severe is CVE-2020-9484?

CVE-2020-9484 has a CVSS score of 7/10, rated HIGH. Immediate patching is strongly recommended.

Which packages are affected by CVE-2020-9484?

CVE-2020-9484 affects the following packages: org.apache.tomcat:tomcat-catalina (Maven), org.apache.tomcat:tomcat-catalina (Maven), org.apache.tomcat:tomcat-catalina (Maven), org.apache.tomcat:tomcat-catalina (Maven), org.apache.tomcat.embed:tomcat-embed-core (Maven), org.apache.tomcat.embed:tomcat-embed-core (Maven), org.apache.tomcat.embed:tomcat-embed-core (Maven), org.apache.tomcat.embed:tomcat-embed-core (Maven). Ecosystems affected: Maven.

How do I fix CVE-2020-9484?

Update org.apache.tomcat:tomcat-catalina to 10.0.0-M5 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2020-9484 is resolved across your whole dependency graph.

How do I detect CVE-2020-9484 in my Maven dependencies?

Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for org.apache.tomcat:tomcat-catalina. O3's reachability analysis confirms whether the vulnerable code path is actually invoked in your application, so you act on real exposure instead of every transitive match.

How do I mitigate CVE-2020-9484 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.

How does O3 Security protect against CVE-2020-9484?

O3 pinpoints whether CVE-2020-9484 is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.

Is CVE-2020-9484 actively exploited in the wild?

Yes. There are 27 known exploit references for CVE-2020-9484, including 15 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-2020-9484?

CVE-2020-9484 has an EPSS (Exploit Prediction Scoring System) score of 56.6%, placing it in the 99th 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.

What type of vulnerability is CVE-2020-9484?

CVE-2020-9484 is classified as Deserialization of Untrusted Data (CWE-502). This weakness type describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation. This is a high-impact weakness class that often enables remote code execution or data exposure.

Is there exploit tooling available for CVE-2020-9484?

A Nuclei detection template exists for CVE-2020-9484, 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-2020-9484 published, and has it been updated?

CVE-2020-9484 was published on May 20, 2020 and was last updated on July 8, 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

Not in CISA KEV

HIGH severity

CVE-2020-9484

HIGH

CVE-2020-9484 is a high-severity (CVSS 7) Deserialization of Untrusted Data vulnerability in org.apache.tomcat:tomcat-catalina. 27 public exploit references exist, so weaponization risk is real. O3 Security confirms whether CVE-2020-9484 is actually reachable in your code before you act, and blocks exploitation at runtime until you patch.

Potential remote code execution in Apache Tomcat

Also known asBIT-tomcat-2020-9484GHSA-344f-f5vg-2jfj

Published

May 20, 2020

Updated

Jul 8, 2026

Affected

8 pkgs

Patched

8 / 8

Exploits

27 known

Exploitation data as of Jul 31, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

EPSS Exploitation Probability

via FIRST.org ↗

56.6%probability of exploitation in next 30 days

High Risk0.00%

Lower risk than most CVEs99th percentile — riskier than 99% of all scored CVEsHighest risk

EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.

How urgent is this, really

CVE-2020-9484 plotted by exploitation likelihood (EPSS) against impact (CVSS). The shaded corner — EPSS 50%+ and CVSS 7.0+ — is where this CVE sits: patch-first territory.

Where this sits among everything scored

Of 365,017 CVEs with a current EPSS score, this one falls in the 50–90% band (highlighted). Real counts from FIRST.org, not a sample — log-scaled since the landscape is heavily right-skewed.

Real-World Exposure

8 pkgs affected

☕org.apache.tomcat:tomcat-catalina☕org.apache.tomcat:tomcat-catalina☕org.apache.tomcat:tomcat-catalina☕org.apache.tomcat:tomcat-catalina☕org.apache.tomcat.embed:tomcat-embed-core☕org.apache.tomcat.embed:tomcat-embed-core☕org.apache.tomcat.embed:tomcat-embed-core☕org.apache.tomcat.embed:tomcat-embed-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

When using Apache Tomcat versions 10.0.0-M1 to 10.0.0-M4, 9.0.0.M1 to 9.0.34, 8.5.0 to 8.5.54 and 7.0.0 to 7.0.103 if a) an attacker is able to control the contents and name of a file on the server; and b) the server is configured to use the PersistenceManager with a FileStore; and c) the PersistenceManager is configured with sessionAttributeValueClassNameFilter="null" (the default unless a SecurityManager is used) or a sufficiently lax filter to allow the attacker provided object to be deserialized; and d) the attacker knows the relative file path from the storage location used by FileStore to the file the attacker has control over; then, using a specifically crafted request, the attacker will be able to trigger remote code execution via deserialization of the file under their control. Note that all of conditions a) to d) must be true for the attack to succeed.

Affected Packages

8 total 8 fixed

Ecosystem	Package	Vulnerable range	Fix
☕Maven	`org.apache.tomcat:tomcat-catalina`	≥ 10.0.0-M1&&< 10.0.0-M5	10.0.0-M5
☕Maven	`org.apache.tomcat:tomcat-catalina`	≥ 9.0.0&&< 9.0.35	9.0.35
☕Maven	`org.apache.tomcat:tomcat-catalina`	≥ 8.0.0&&< 8.5.55	8.5.55
☕Maven	`org.apache.tomcat:tomcat-catalina`	≥ 7.0.0&&< 7.0.104	7.0.104
☕Maven	`org.apache.tomcat.embed:tomcat-embed-core`	≥ 10.0.0-M1&&< 10.0.0-M5	10.0.0-M5
☕Maven	`org.apache.tomcat.embed:tomcat-embed-core`	≥ 9.0.0&&< 9.0.35	9.0.35

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.