VulnerabilityPublished 23 Sep 2026

CVE-2026-87022: Apache Tomcat · Improper Handling of Length Parameter Inconsistency

Affects Apache TomcatSource CVE Database V5

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Not known to be exploited · CVSS 7.5 High · fixed in 11.0.26 : patch Apache Tomcat soon.

Data as of 6 Nov 2026, 23:24 UTC

CVSS 3.1 base score

7.5High

How severe the flaw is on the 0–10 CVSS scale.

EPSS: 0.5% chance of exploitation in 30 days – higher than 45% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
Patch: Available – fixed in 11.0.26

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N

Attack Vector: Network
Attack Complexity: Low
Privileges Required: None
User Interaction: None
Scope: Unchanged
Confidentiality: None
Integrity: High
Availability: None

Bold values are the worst case: easiest to exploit or largest impact.

Attack Vector: Network: The vulnerable component is bound to the network stack and the set of possible attackers extends beyond the other options listed, up to and including the entire Internet. Such a vulnerability is often termed 'remotely exploitable' and can be thought of as an attack being exploitable at the protocol level one or more network hops away (e.g., across one or more routers).
Attack Complexity: Low: Specialized access conditions or extenuating circumstances do not exist. An attacker can expect repeatable success against the vulnerable component.
Privileges Required: None: The attacker is unauthorized prior to attack, and therefore does not require any access to settings or files to carry out an attack.
User Interaction: None: The vulnerable system can be exploited without any interaction from any user.
Scope: Unchanged: An exploited vulnerability can only affect resources managed by the same security authority. In this case, the vulnerable component and the impacted component are either the same, or both are managed by the same security authority.
Confidentiality: None: There is no loss of confidentiality within the impacted component.
Integrity: High: There is a total loss of integrity, or a complete loss of protection. For example, the attacker is able to modify any/all files protected by the impacted component. Alternatively, only some files can be modified, but malicious modification would present a direct, serious consequence to the impacted component.
Availability: None: There is no impact to availability within the impacted component.

Definitions: FIRST CVSS v3.1 specification.

Exploitation evidence

Disclosed: evidence found.
CVE published 23 Sep 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponized: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 7 Nov 2026.

Disclosed: The CVE record is public on cve.org. Its publication is t = 0.
Detectable: A public nuclei template can find exposed instances, for defenders and attackers alike.
Weaponized: A Metasploit exploit module or Exploit-DB entry exists (Metasploit scanner modules do not count), or CISA SSVC or the CVSS exploit maturity reports a public proof of concept.
Exploited in the wild: CISA KEV lists it, CISA SSVC rates exploitation active, or a source reports attacks.
Observed by OffSeq Mirage: OffSeq Mirage honeypot sensors recorded attack traffic for this CVE, or found exposed hosts without attack traffic.

Moments are spaced evenly, not to scale; a dashed line marks a gap of six months or more. Deltas count from t = 0. Sources that give only a date (CISA KEV, Exploit-DB, or a time of exactly 00:00Z) read “same day” rather than hours. Metasploit modules carry the flaw’s disclosure date, not their release date, and nuclei templates carry no date, so both appear above but not on the timeline.

What to do

Affected software

Product	Affected	Fixed in
Apache Software FoundationApache Tomcat	Affected >=11.0.0-M1 <=11.0.25 >=10.1.0-M1 <=10.1.59 >=9.0.0.M1 <=9.0.121 >=8.5.0 <=8.5.100 >=7.0.56 <=7.0.109	Fixed in–
Mavenorg.apache.tomcat/tomcat`pkg:maven/org.apache.tomcat/tomcat`Other threats	Affected >=7.0.56 <=7.0.109 >=8.5.0 <=8.5.100 >=9.0.0-M1 <=9.0.121 >=10.1.0-M1 <=10.1.59 >=11.0.0-M1 <=11.0.25	Fixed in–

Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.

AI-suggested

Users should upgrade affected Apache Tomcat versions to 11.0.26, 10.1.60, or 9.1.22, where the vulnerability has been fixed. Applying these official updates is the recommended and effective mitigation. No additional vendor advisories indicate alternative mitigations or that no action is required.

Description

CVE-2026-87022 is a high-severity vulnerability in Apache Tomcat involving improper handling of length parameter inconsistencies when using per-message-deflate in WebSocket communications. This flaw allows WebSocket message smuggling, potentially enabling attackers to interfere with message integrity. The vulnerability affects multiple versions of Apache Tomcat, including 11.0.0-M1 through 11.0.25, 10.1.0-M1 through 10.1.59, 9.0.0.M1 through 9.0.121, and some older end-of-support versions. Fixed versions are available, and users are advised to upgrade to 11.0.26, 10.1.60, or 9.1.22 to mitigate the issue.

Impact

The vulnerability allows attackers to perform WebSocket message smuggling by exploiting inconsistencies in length parameter handling when per-message-deflate is used. This can lead to message injection or manipulation within WebSocket communications, impacting the integrity of data transmitted over affected Apache Tomcat servers. The CVSS score of 7.5 (high) reflects the potential for significant impact on message integrity without requiring privileges or user interaction.

Summary

CVE-2026-87022 is a vulnerability in Apache Tomcat caused by improper handling of length parameter inconsistencies in WebSocket frames when per-message-deflate compression is enabled. This flaw can be exploited to perform WebSocket message smuggling, which may allow an attacker to manipulate or inject messages within a WebSocket connection. The vulnerability affects Apache Tomcat versions from 11.0.0-M1 through 11.0.25, 10.1.0-M1 through 10.1.59, 9.0.0.M1 through 9.0.121, and older unsupported versions such as 8.5.0 through 8.5.100 and 7.0.56 through 7.0.109. The Apache Software Foundation has addressed this issue in versions 11.0.26, 10.1.60, and 9.1.22.

CWE-130Improper Handling of Length Parameter Inconsistency (opens in a new tab)
Base weakness
The product parses a formatted message or structure, but it does not handle or incorrectly handles a length field that is inconsistent with the actual length of the associated data.
Implementation
When processing structured incoming data containing a size field followed by raw data, ensure that you identify and resolve any inconsistencies between the size field and the actual size of the data.
Implementation
Do not let the user control the size of the buffer.
Implementation
Validate that the length of the user-supplied data is consistent with the buffer size.
OWASP Cheat Sheets
XML Security (opens in a new tab)
Mass Assignment (opens in a new tab)
OWASP ASVS 4.0.3
V13.3.1 (opens in a new tab)
V5.1.4 (opens in a new tab)
V5.1.3 (opens in a new tab)
Attack patterns
Buffer Overflow via Parameter Expansion (opens in a new tab)
From MITRE CWE, MITRE CAPEC and OWASP (Top 10, OpenCRE).

References

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Exploitation evidence

What to do

Affected software

Description

AI analysisMachine-generated, updated 17 Oct 2026, 23:23 UTC

WeaknessesCWE-130

Technical details

References

Community reviews

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