CVE-2020-9484
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.
- CVSS
- 7.0High
- Exploited in the wild
- Not knownUnvetted proof-of-concept code on GitHub; not in CISA KEV
- EPSS
- 55.5%chance of exploitation in the next 30 daystop 1% of scored CVEsFIRST score of 11 Nov 2026
- Fix
- Patch availablesee the advisories in the references
- Published
- 20 May 2020analysed here 12 Nov 2026
Summary
Triage
The summary, impact and action text on this page are written by our AI analysis pipeline, or taken from the NVD description when a CVE was imported from NVD. They are not the vendor's wording: check them against the sources. A longer AI executive summary and technical analysis are generated for signed-in accounts on the Max plan.
Affected products
| Product | Affected versions | Vendor says fixed in |
|---|---|---|
| Apache Tomcat | Apache Tomcat 10.0.0-M1 to 10.0.0-M4, 9.0.0.M1 to 9.0.34, 8.5.0 to 8.5.54, 7.0.0 to 7.0.103Vendor says fixed in: not stated |
As published in the CVE Program record. A version outside these ranges is not a statement that it is unaffected — vendors sometimes understate a range, and distribution-backported builds carry upstream numbers that do not reflect what was patched into them.
Products named in our analysis
- apache:tomcat
- debian:debian_linux
- opensuse:leap
- fedoraproject:fedora
- canonical:ubuntu_linux
- oracle:agile_engineering_data_management
- oracle:agile_product_lifecycle_management
- oracle:communications_cloud_native_core_binding_support_function
- oracle:communications_cloud_native_core_policy
- oracle:communications_diameter_signaling_router
- oracle:communications_element_manager
- oracle:communications_instant_messaging_server
- oracle:communications_session_report_manager
- oracle:communications_session_route_manager
- oracle:database
- oracle:fmw_platform
- oracle:hospitality_guest_access
- oracle:instantis_enterprisetrack
- oracle:managed_file_transfer
- oracle:mysql_enterprise_monitor
- oracle:retail_order_broker
- oracle:siebel_apps_-_marketing
- oracle:siebel_ui_framework
- oracle:transportation_management
- oracle:workload_manager
- mcafee:epolicy_orchestrator
Fix and mitigation
WAF and other mitigations
Can a WAF block it? No. The attack needs local access to the machine, so a WAF is not on its path.
Also consider: allow-list classes · patch
Based on the attack vector (local or physical access). We check Cloudflare, AWS, Google Cloud Armor and Azure; for Akamai, Imperva, Fastly, F5, ask your vendor.
Remediation steps (AI-written)
Step-by-step remediation is generated for accounts on the Max plan, for CVEs that match a technology in their stack. Add this technology to your stack to see the fix checklist.
Exploitation evidence
- CISA KEV catalog
- Not listed as of our last sync.
- Public exploit code
- Unvetted proof-of-concept code on GitHub: 17 GitHub proofs of concept · 1 Nuclei template
- CISA SSVC
- exploitation none, automatable no, technical impact totalAssessed by CISA 8 Oct 2026 (SSVC 2.0.3). Exploitation is none, poc (public proof of concept) or active.
Nuclei
- Apache Tomcat Remote Command Executiondetection template, high
GitHub proofs of concept
- threedr3am/tomcat-cluster-session-sync-exp214 stars
- masahiro331/CVE-2020-9484126 stars
- IdealDreamLast/CVE-2020-948452 stars
- PenTestical/CVE-2020-948435 stars
and 13 more repositories
Listed so you can judge urgency, not as a recommendation to run anything. GitHub “proofs of concept” are unvetted: some are fake or carry malware. Exploit-DB marks the entries its staff verified.
Timeline
- 19 May 2020First proof-of-concept repository on GitHub (unvetted)
- 20 May 2020Published2 days later
- 8 Oct 2026CISA SSVC assessment: exploitation none2,332 days (about 6 years) later
- 8 Oct 2026CVE record last updatedsame day later
- 12 Nov 2026Analysed by vulneraibility.com35 days later
CVSS vector
CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H
| Metric | Value | What it means |
|---|---|---|
| Attack vector | LocalLocal access required (shell, logged-in user). | Local access required (shell, logged-in user). |
| Attack complexity | HighNeeds specific conditions, a race or a particular configuration. | Needs specific conditions, a race or a particular configuration. |
| Privileges required | LowThe attacker needs basic user privileges. | The attacker needs basic user privileges. |
| User interaction | NoneNo victim action needed. | No victim action needed. |
| Scope | UnchangedImpact stays within the vulnerable component. | Impact stays within the vulnerable component. |
| Confidentiality | HighTotal data disclosure possible. | Total data disclosure possible. |
| Integrity | HighComplete modification possible. | Complete modification possible. |
| Availability | HighFull outage possible. | Full outage possible. |
Common questions
Is CVE-2020-9484 being exploited?
Not confirmed. CVE-2020-9484 does not appear in CISA's Known Exploited Vulnerabilities catalog, which records only exploitation that has been observed and reported publicly. That is evidence of absence of a report, not evidence the flaw is unattacked. EPSS currently estimates a 56% probability of exploitation in the next 30 days.
How severe is CVE-2020-9484?
CVE-2020-9484 is rated High with a CVSS score of 7.0. Severity describes how bad exploitation would be, not how likely it is: pair it with exploitation evidence before deciding what to patch first.
Is there a patch for CVE-2020-9484?
Yes. A fix has been recorded for CVE-2020-9484. The vendor advisory is the authority on the exact fixed version — apply it from there rather than from a summary.
What does CVE-2020-9484 affect?
CVE-2020-9484 affects apache:tomcat, debian:debian_linux, opensuse:leap, fedoraproject:fedora, and 22 further products or versions. Confirm the exact affected versions against the vendor advisory before deciding you are exposed.
Exploitation status reflects CISA's KEV catalog as we last synced it. Check the catalog directly.
References
42 references in the CVE record, grouped by the tags the record gives them.
Advisories (7)
- lists.opensuse.org /opensuse-security-announce/2020-05/msg00057.html
- security.gentoo.org /glsa/202006-21
- lists.fedoraproject.org /archives/list/package-announce%40lists.fedoraproject.org/message/WJ7XHKWJWDNWXU
- lists.fedoraproject.org /archives/list/package-announce%40lists.fedoraproject.org/message/GIQHXENTLYUNOE
- debian.org /security/2020/dsa-4727
- usn.ubuntu.com /4448-1/
Show 1 more
- usn.ubuntu.com /4596-1/
Other links (35)
- lists.apache.org /thread.html/rf70f53af27e04869bdac18b1fc14a3ee529e59eb12292c8791a77926%40%3Cuser
- lists.debian.org /debian-lts-announce/2020/05/msg00020.html
- lists.apache.org /thread.html/r26950738f4b4ca2d256597cf391d52d3450fa665c297ea5ca38f5469%40%3Cuser
- lists.apache.org /thread.html/r7bc247fffcb1d58415215c861d2354bd653c86266230d78a93c71ae2%40%3Cdev.
- lists.debian.org /debian-lts-announce/2020/05/msg00026.html
- seclists.org /fulldisclosure/2020/Jun/6
Show 29 more
- lists.apache.org /thread.html/rb1c0fb105ce2b93b7ec6fc1b77dd208022621a91c12d1f580813cfed%40%3Cdev.
- lists.debian.org /debian-lts-announce/2020/07/msg00010.html
- oracle.com /security-alerts/cpujul2020.html
- lists.apache.org /thread.html/r77eae567ed829da9012cadb29af17f2df8fa23bf66faf88229857bb1%40%3Canno
- security.netapp.com /advisory/ntap-20200528-0005/
- packetstormsecurity.com /files/157924/Apache-Tomcat-CVE-2020-9484-Proof-Of-Concept.html
- lists.apache.org /thread.html/r123b3ebe389f46f9d337923f393cdae4d3e9b78d982d706712f0898c%40%3Ccomm
- lists.apache.org /thread.html/raa4123e472175bb052fbba165d37187cea923f755e8f3f30d124cb3f%40%3Ccomm
- lists.apache.org /thread.html/rc8473b08abdf3c16494ed817bec1717a0ee0c8080315bc27db5f21c3%40%3Ccomm
- lists.apache.org /thread.html/rf59c72572b9fee674a5d5cc6afeca4ffc3918a02c354a81cc50b7119%40%3Ccomm
- oracle.com /security-alerts/cpuoct2020.html
- kc.mcafee.com /corporate/index?page=content&id=SB10332
- oracle.com /security-alerts/cpujan2021.html
- lists.apache.org /thread.html/rfe62fbf9d4c314f166fe8c668e50e5d9dd882a99447f26f0367474bf%40%3Cdev.
- lists.apache.org /thread.html/rfe62fbf9d4c314f166fe8c668e50e5d9dd882a99447f26f0367474bf%40%3Canno
- lists.apache.org /thread.html/rfe62fbf9d4c314f166fe8c668e50e5d9dd882a99447f26f0367474bf%40%3Cuser
- lists.apache.org /thread.html/rf6d5d57b114678d8898005faef31e9fd6d7c981fcc4ccfc3bc272fc9%40%3Cdev.
- lists.apache.org /thread.html/rfe62fbf9d4c314f166fe8c668e50e5d9dd882a99447f26f0367474bf%40%3Canno
- openwall.com /lists/oss-security/2021/03/01/2
- lists.apache.org /thread.html/r8dd19c514face6dd85fd4eab0271854883f40c7307926c1f7cd5400c%40%3Ccomm
- oracle.com /security-alerts/cpuApr2021.html
- lists.apache.org /thread.html/r8a2ac0e476dbfc1e6440b09dcc782d444ad635d6da26f0284725a5dc%40%3Cuser
- lists.apache.org /thread.html/rb51ccd58b2152fc75125b2406fc93e04ca9d34e737263faa6ff0f41f%40%3Cuser
- lists.apache.org /thread.html/r11ce01e8a4c7269b88f88212f21830edf73558997ac7744f37769b77%40%3Cuser
- lists.apache.org /thread.html/rc1778b38e74b5b6142414d57623bd55b023a72361f422836782fca3c%40%3Cdev.
- oracle.com //security-alerts/cpujul2021.html
- oracle.com /security-alerts/cpuoct2021.html
- oracle.com /security-alerts/cpujan2022.html
- oracle.com /security-alerts/cpujul2022.html
Where the data on this page comes from
- CVE List (CVE.org): description, affected versions, references; CVE Terms of Use
- NVD: CVSS and CPE data
- CISA Vulnrichment (ADP): SSVC decision points
- FIRST EPSS: exploit probability and percentile
- Nuclei templates: detection templates
- PoC-in-GitHub: GitHub repositories that claim a proof of concept
Summary, impact and triage tags: written by our AI analysis pipeline from the sources above. Check them against the sources.
Similar CVEs
Get CVEs like this by email. Join the free digest: the CVEs we flag as major, all CVSS 8.0 or higher, in up to three emails a day (sent at 05:00, 11:00 and 15:00 UTC). Matching alerts to the products you run needs an account, and accounts are invite-only during the beta.