CVE Intelligence
High

CVE-2020-11996 — A specially crafted sequence of HTTP/2 requests sent to Apache Tomcat 10.0.0-M1 to…

A specially crafted sequence of HTTP/2 requests sent to Apache Tomcat 10.0.0-M1 to 10.0.0-M5, 9.0.0.M1 to 9.0.35 and 8.5.0 to 8.5.55 could trigger high CPU usage for several seconds. If a sufficient number of such requests were made on concurrent HTTP/2 connections, the server could become unresponsive.

Published Jun 26, 2020 · Updated Oct 13, 2026 · Sources: NIST National Vulnerability Database, CVE Program (cve.org) e CISA ADP · CNA: apache

Who exploits it and how urgent it is

A 0–100 score combining confirmed exploitation, ransomware and APT use, public exploits, EPSS and severity.

No exploitation signal in the sources consulted so far.
How the score was calculated
  • EPSS 26.7% (30-day exploitation probability)+15
  • Technical severity (high)+6
  • Automatable exploitation (SSVC)+3

The score orders the patch queue; it does not replace your asset context (internet exposure, criticality, compensating controls).

Triage

Is it exploited, how likely is exploitation, what does it touch, and how severe do the sources call it.

Exploitation
Not confirmed
Not in CISA KEV — an absence of record, not proof it is unexploited.
EPSS FIRST
26.7%
ahead of 98% of scored CVEs · Oct 14, 2026
Affects
Apache Software Foundation
Tomcat and 7 more
CVSS base
7.5
High · 1 source(s)

CISA SSVC assessment CISA

Three decision points CISA publishes for the CVEs it assesses (SSVC 2.0.3). A stakeholder decision, not a severity score.

Exploitation
None
none · proof-of-concept · active
Automatable
Yes
can an attacker script the kill-chain steps
Technical impact
Partial
partial · total control of the vulnerable component

Remediation

Fixes and mitigations documented by the sources — linked to the original advisory.

No fix documented by the sources we poll. That does not mean none exists: check the vendor advisory.

First 24 hours

Ordered from the record’s own fields — exposure first, because you cannot patch what you have not found. A rule-generated starting point.

  1. Identify exposed assets running the affected vendor/product/version combinations (Apache Software Foundation Tomcat, Canonical Ubuntu Linux, Debian Debian Linux…).
  2. The attack is network-based and needs no privileges: restrict exposure (ACLs, VPN, WAF) until patched.
  3. No fix documented in the sources: reduce exposure and monitor the vendor advisory.
  4. EPSS ahead of 98% of scored CVEs: prioritize it in the patch queue.
  5. Search available logs for exploit probes, errors and authentication anomalies.

Affected scope

Vendor, product and versions as the sources word them.

VendorProductVersionsStatusSource
Apache Software Foundation Tomcat version 9.0.0-milestone7version 9.0.0-milestone23version 9.0.0-milestone24version 9.0.0-milestone25version 9.0.0-milestone26version 9.0.0-milestone27version 9.0.0-milestone3version 9.0.0-milestone4
and 26 more version 9.0.0-milestone5version 9.0.0-milestone6version 9.0.0-milestone22version 9.0.0-milestone8version 9.0.0-milestone9version 10.0.0-milestone1version 10.0.0-milestone2version 10.0.0-milestone3version 10.0.0-milestone4version 10.0.0-milestone5version 9.0.0-milestone14≥ 8.5.0 and ≤ 8.5.55≥ 9.0.0 and ≤ 9.0.35version 9.0.0-milestone1version 9.0.0-milestone10version 9.0.0-milestone11version 9.0.0-milestone12version 9.0.0-milestone13version 9.0.0-milestone15version 9.0.0-milestone16version 9.0.0-milestone17version 9.0.0-milestone18version 9.0.0-milestone19version 9.0.0-milestone2version 9.0.0-milestone20version 9.0.0-milestone21
Vulnerable NIST National Vulnerability Database
Apache Software Foundation Tomcat version 10.0.0-M1 to 10.0.0-M5version 9.0.0.M1 to 9.0.35version 8.5.0 to 8.5.55 Vulnerable CVE Program (cve.org) e CISA ADP
Canonical Ubuntu Linux version 20.04 Vulnerable NIST National Vulnerability Database
Debian Debian Linux version 10.0version 9.0 Vulnerable NIST National Vulnerability Database
Netapp Oncommand System Manager version 3.0version 3.1.3 Vulnerable NIST National Vulnerability Database
Opensuse Leap version 15.1version 15.2 Vulnerable NIST National Vulnerability Database
Oracle Mysql Enterprise Monitor ≤ 8.0.21 Vulnerable NIST National Vulnerability Database
Oracle Siebel Ui Framework ≤ 20.12 Vulnerable NIST National Vulnerability Database
Oracle Workload Manager version 12.2.0.1version 18cversion 19c Vulnerable NIST National Vulnerability Database

Attack characteristics

The CVSS vector, decoded. It describes the attack, not your exposure to it.

Attack vector
Network
Attack complexity
Low
Privileges required
None
User interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
High

Every base score collected

Sources score independently and may disagree; each row says who scored it and under which version.

ScoreVersionSeverityExpl.ImpactScored by
7.5 CVSS 3.1 High 3.9 3.6 nvd@nist.gov via NIST National Vulnerability Database
5.0 CVSS 2.0 Medium 10.0 2.9 nvd@nist.gov via NIST National Vulnerability Database
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H (score shown at the top: nvd@nist.gov)

EPSS over time FIRST

Oct 13, 2026 → Oct 14, 2026 · 2 reading(s) · max 26.70%

Detection

Read off the CVSS vector and the weakness class. Starting points, not tested rules.

  • Prioritize edge telemetry for the network-reachable component (proxy, WAF, IDS/IPS).
web/proxy/WAF logsnetwork IDS/IPS

Timeline

What happened to this CVE, newest first.

  • 2026
  • Affected products added · apache/apache tomcat
    Oct 13, 2026 · CVE Program (cve.org) e CISA ADP
  • SSVC assessment updated
    Oct 13, 2026 · CVE Program (cve.org) e CISA ADP
  • Record published
    Oct 13, 2026
  • CVSS changed · 7.5
    Oct 13, 2026 · NIST National Vulnerability Database
  • Source status changed · → Modified
    Oct 13, 2026 · NIST National Vulnerability Database
  • Record created in this database
    Oct 13, 2026 · NIST National Vulnerability Database
  • 2020
  • CVE published
    Jun 26, 2020 · apache

Source activity

Repeated readings are counted rather than listed.

  • 1× Official description updated · Oct 13, 2026 – Oct 13, 2026

References

24 on the record

Elsewhere on this site

Apache Software Foundation
every CVE for this vendor

Related CVEs (same products)

  • CVE-2026-73180 Insufficient Session Expiration vulnerability in Apache Tomcat meant that if the session… Aug 25, 2026
  • CVE-2026-65637 Improper Input Validation in Apache Software Foundation Tomcat Aug 25, 2026
  • CVE-2026-65183 TOCTOU Race Condition in Apache Software Foundation Tomcat Aug 25, 2026
  • CVE-2026-65905 Authentication Bypass by Capture-replay in Apache Software Foundation Tomcat Aug 25, 2026
  • CVE-2026-65927 Off-by-one Error vulnerability in Apache Tomcat impacting the [N] flag on the rewrite… Aug 25, 2026
  • CVE-2026-68569 Improper Authentication in Apache Software Foundation Tomcat Aug 25, 2026

Not in any source we poll

Listed rather than left blank: an empty field and an unmeasured one look identical on screen, and only one is a reason to look elsewhere.

  • No fixed version, patch or mitigation documented.
  • No CWE classification.
  • No confirmed IOCs, IP addresses, domains, file hashes, or malware artifacts supplied.
  • No organization-specific asset inventory, compensating-control status, or patch deployment evidence supplied.
  • No exploit packet captures, log samples, or incident case IDs supplied.

Answered from this record

Text assembled only from the fields above — no additional claims.

What should defenders know first?

CVE-2020-11996 is "A specially crafted sequence of HTTP/2 requests sent to Apache Tomcat 10.0.0-M1 to…", rated High. It affects Tomcat (Apache Software Foundation); versions are in the scope table. It is not in CISA KEV, which does not rule out exploitation. CVSS 7.5 describes technical severity. EPSS 26.70% estimates the probability of exploitation in 30 days; neither replaces your asset context. First verify whether exposed or business-critical assets run the affected versions, apply vendor fixes or mitigations, and preserve logs for review.

Comments

Moderated technical discussion. Read the community guidelines.

No comments yet.

Sign in or create an account to comment and suggest corrections.