7.5

CVSS Score

3.1

-

CVSS Score

Basic Information

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CVE-2021-3859

CVE-2021-3859: Undertow vulnerable to Denial of Service (DoS) attacks

Undertow client side invocation timeout raised when calling over HTTP2, this vulnerability can allow attacker to carry out denial of service (DoS) attacks in versions less than 2.2.15 Final.

(GitHub Advisory)

Miggo Vulnerability Database

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CVE-2021-3859

CVE-2021-3859:

7.5

CVSS Score

3.1

-

CVSS Score

Basic Information

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Technical Details

Package Name	Ecosystem	Vulnerable Versions	First Patched Version
io.undertow:undertow-core	maven	< 2.2.15	2.2.15

Technical Details

Vulnerability Intelligence
Miggo AI

Root Cause Analysis

The vulnerability stems from two key issues: 1) In Http2Channel.java, the parseFrame method didn't properly handle continuation frames across multiple packets, as shown by the addition of a do-while loop in the patch to process continuation data. 2) In HpackEncoder.java, the encode method had incorrect iterator management that could leave headers unprocessed. The commit directly modifies these functions to add proper continuation frame handling and iterator advancement, aligning with the CWE-400 (Uncontrolled Resource Consumption) description. The test case H2CUpgradeContinuationTestCase added in the patch validates these fixes by forcing continuation frame scenarios.

Vulnerable functions

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WAF Protection Rules

WAF Rule

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Reasoning

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