NVD / CVE Program· CNA GitHub_M

CVE-2022-41952: Uncontrolled Resource Consumption in Matrix Synapse

Noroxi assessment

Priority: Monitor (action score 21/100)

The sources we track (CISA KEV, Exploit-DB, Metasploit, Nuclei, GitHub) show no public exploit code or exploitation in the wild.
Probability of exploitation in the next 30 days: 0.90% (FIRST EPSS); higher than 59.5% of all records.
Anyone who can reach it over the internet can trigger it. No account or password is required. No user action is required. No special conditions are required; it is repeatable.
According to CISA the attack is automatable: targets can be found by mass scanning.
Fixed version: matrix-synapse (PyPI) 1.53.0.

Low priority for now. Upgrade to matrix-synapse (PyPI) 1.53.0 or later.

Generated automatically from the record's data: CVSS (NVD and CNA), CISA KEV and SSVC, FIRST EPSS, exploit sources, fixed versions. How we calculate it

Primary sources: NVD · CVE.org · FIRST EPSS

Synapse before 1.52.0 with URL preview functionality enabled will attempt to generate URL previews for media stream URLs without properly limiting connection time. Connections will only be terminated after `max_spider_size` (default: 10M) bytes have been downloaded, which can in some cases lead to long-lived connections towards the streaming media server (for instance, Icecast). This can cause excessive traffic and connections toward such servers if their stream URL is, for example, posted to a large room with many Synapse instances with URL preview enabled. Version 1.52.0 implements a timeout mechanism which will terminate URL preview connections after 30 seconds. Since generating URL previews for media streams is not supported and always fails, 1.53.0 additionally implements an allow list for content types for which Synapse will even attempt to generate a URL preview. Upgrade to 1.53.0 to fully resolve the issue. As a workaround, turn off URL preview functionality by setting `url_preview_enabled: false` in the Synapse configuration file.

MediumCVSS 5.3 · v3.1—No exploit Fix available

Published: Nov 22, 2022
Updated: Jun 17, 2026
EPSS: 0.9% · 59th percentile
CWE: CWE-400

Report tools

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Action score

Monitor

Low priority for now.

CVSS: 21 / 40 · 5.3 / 10
CISA KEV: 0 / 30 · Not listed
EPSS: 0 / 30 · 0.9%

CISA SSVC decision

Exploitation: none
Automatable: yes
Technical impact: partial

Vulnrichment: CISA's decision-tree inputs.

CNA vs NVD score

NVD: 5.3
CNA · GitHub_M: 6.5; 1.2 point gap

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

The score given by the assigning authority versus NVD’s independent score. A gap means the severity is contested.

Get told when this record changes

Not in KEV: no record of exploitation in the wild
No public exploit code on record
A fix has been released

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Noroxi analysis

What does it mean in your environment?

The assessment above is generated automatically from the record's data; it doesn't know your environment. Our team verifies on your systems whether this vulnerability is actually exploitable and which mitigation is enough.

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Affected systems

Is your version affected?

Pick the product and type the version you run. It's compared with this record's version ranges in your browser; the version isn't sent anywhere.

Vendor	Product	CPE
matrix	synapse	cpe:2.3:a:matrix:synapse

Affected versions

NVD version ranges (for catalog products). Add the product to your stack with a version and matching uses these.

matrix synapsebefore 1.53.0

Versions reported by the vendor

Affected version ranges reported by the assigning authority (GitHub_M). Independent of NVD's CPE analysis and usually ahead of it.

matrix-org synapse
- < 1.53.0affected

Package-level exposure

OSV and GitHub Advisory data: ecosystem, package and range. SBOM matching uses this table.

Ecosystem	Package	Affected range	Fix
PyPI	matrix-synapse	before 1.53.0	1.53.0

Same product

matrix: all records

Other highest-scoring records for the same primary product.

CVE-2019-18835Matrix Synapse before 1.5.0 mishandles signature checking on some federation APIs.
39Monitor
CVE-2018-16515Matrix Synapse before 0.33.3.1 allows remote attackers to spoof events and possibly have unspecified other impacts by leveraging improper tr
35Monitor
CVE-2024-52815Synapse allows a a malformed invite to break the invitee's `/sync`
34Monitor

Published before and after this one in the same product

← EarlierCVE-2022-31052Jun 28, 2022 · URL previews can crash Synapse media repositories or Synapse monoliths
26Monitor
← EarlierCVE-2022-31152Sep 2, 2022 · Synapse vulnerable to denial of service (DoS) due to incorrect application of event authorization rules
30Monitor
Later →CVE-2022-39335May 26, 2023 · Synapse does not apply enough checks to servers requesting auth events of events in a room
20Monitor

Remediation

Which version to upgrade to

Fix versions compiled from the vendor, package registries and Microsoft. Verify the vendor's note before upgrading.

Product / package	Fixed version	Source
debian:matrix-synapse	1.53.0-1 · Debian:14	Package registry (OSV)
PyPI:matrix-synapse	1.53.0	Package registry (OSV)

Exploit status

No known public exploit

No public exploit has been observed yet. That doesn't mean you're safe, only that the bar is a little higher.

Research context

For pentesters and researchers: attack profile, score disagreement, timeline, patch commits, credits, variant and chain candidates, bug bounty scope. All derived from existing data; no exploit code.

Timeline

From publication to today: proof of concept, Metasploit module, CISA KEV and fix record. Dates are as reported by the sources.

No dated events beyond publication.

EPSS, last 120 days

FIRST EPSS daily score; only changes of 0.01 or more are recorded (step chart).

Patch and commit links

Commit, PR and diff links among the references. A starting point for patch-diffing and variant hunting; fixes, not exploits.

Credits

All researchers

Finders, reporters and analysts named in the CNA record. Click a name for that researcher’s other records.

No credits in the CNA record.

Variant candidates

Same product, same weakness class, within 18 months. If the patch missed the root cause, the sibling bug is here.

No nightly-computed relations.

Chain candidates

An authentication bypass and a privilege-requiring bug in the same product, published close together: combined they may become an unauthenticated path.

—

Bug bounty scope

No known public program.

Source: bounty-targets-data (public HackerOne, Bugcrowd, Intigriti, YesWeHack listings).

Technical details

Attack conditions

Anyone who can reach it over the internet can trigger it.
No account or password is required.
No user action is required.
No special conditions are required; it is repeatable.

If successful

Confidentiality: none
Integrity: none
Availability: low · the service can be disrupted

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

Weakness class (CWE)

CWE-400 · Uncontrolled Resource Consumption

CVSS vector

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

nvd-primary

Root cause

Code that parses nested structures sets no depth or size limit. A small input can turn into a disproportionate processing load.

The bug in code

The whole CWE-400 class

A representative example of this vulnerability class. Not the vendor's source code; it shows the faulty pattern and its fix.

Vulnerable

1function expand(node) {
2  return node.children.map(expand);
3}

Fixed

1const MAX_DEPTH = 32;
2function expand(node, depth = 0) {
3  if (depth > MAX_DEPTH) throw new Error("too deep");
4  return node.children.map((c) => expand(c, depth + 1));
5}

Attack context

MITRE CAPEC attack patterns and ATT&CK techniques for this weakness class (CWE). A starting point for detection rules and threat hunting.

Attack patterns (CAPEC)

ATT&CK techniques

Endpoint Denial of ServiceT1499

Change log

Fix✗ → ✓Sep 28, 2026, 10:45 PM UTC

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References

github.com/matrix-org/synapse/pull/11784

Show all references (4 more)

Vendor advisories and official records. Exploit/PoC links are deliberately left out.

All records