CVE-2022-31052Network attack vector

Process crash via unbounded HTML text traversal

Published Jun 28, 2022 · Updated Apr 23, 2025

Uncontrolled recursion in Matrix.org Synapse before 1.61.1 allows remote authenticated users to crash the process through URL previews. The preview_html.py _iterate_over_text function builds an unbounded nested itertools.chain traversal while extracting text from attacker-controlled HTML, exhausting available stack space. Direct access requires an authenticated homeserver account and url_preview_enabled set to true; remote attackers can instead induce an automatic preview through a local user's client.

CVSS severity6.5
Medium
EPSS probability1.66%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Uncontrolled recursion in Matrix.org Synapse before 1.61.1 allows remote authenticated users to crash the process through URL previews. The preview_html.py _iterate_over_text function builds an unbounded nested itertools.chain traversal while extracting text from attacker-controlled HTML, exhausting available stack space. Direct access requires an authenticated homeserver account and url_preview_enabled set to true; remote attackers can instead induce an automatic preview through a local user's client.

The record

CVE
CVE-2022-31052
Published
Jun 28, 2022
Updated
Apr 23, 2025
Vendor
Matrix.org
Product
Synapse
Classifications
CWE-674, T1499.004
Attack vector
network
Privileges
authenticated

Timeline

How it unfolded

  1. Jun 28, 2022CVE publishedPublication date reported by the CVE source.
  2. Apr 23, 2025Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=< 1.61.1

What conditions does exploitation require?

Attack vectornetwork
Required privilegesauthenticated

What is affected?

Matrix.org · Synapseversion=< 1.61.1

Published CVSS scores

3.5NIST NVDAV:N/AC:M/Au:S/C:N/I:N/A:P
6.5GitHub, Inc.CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-674Uncontrolled Recursion
T1499.004Endpoint Denial of Service

Public exploit references

No public exploit references are available in this record.

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Technologies

Your stack

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Your stack

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