GHSA-7565-cq32-vx2x CVE-2023-42453 PYSEC-2023-180

matrix-synapse vulnerable to improper validation of receipts allows forged read receipts

Medium PyPI

Severity: 0.0 / 10; Medium · CVSS 4.0
Exploit chance (EPSS): 0.78%; Chance of exploitation in the next 30 days. Higher than 55.83% of scored vulnerabilities.
Known exploited: No; Not in CISA's catalog
Weakness: CWE-285 Improper Authorization
Fix: 1.93.0; Upgrade matrix-synapse to this version or later

Description

Impact

Users were able to forge read receipts for any event (if they knew the room ID and event ID). Note that the users were not able to view the events, but simply mark it as read. This could be confusing as clients will show the event as read by the user, even if they are not in the room.

Patches

https://github.com/matrix-org/synapse/pull/16327

Workarounds

There is no workaround.

Affected versions

PyPI

Package	Vulnerable	Fixed in
matrix-synapse	`>= 0.34.0, < 1.93.0`	`1.93.0`
matrix-synapse	`>= 1.34.0, < 1.93.0`	`1.93.0`

How to fix

Move to the fixed version or later with your package manager, update the lockfile, and run your tests. If the package only arrives through another dependency, upgrade that dependency first. If none of its releases pulls a fixed version yet, force the version with your package manager's override.

matrix-synapse PyPI → `1.93.0`

pip

pip install --upgrade "matrix-synapse>=1.93.0"

poetry

poetry add "matrix-synapse>=1.93.0"

uv

uv add "matrix-synapse>=1.93.0"

Severity breakdown

CVSS 4.0 0.0

CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N

Attack vector: Network
Attack complexity: Low
Attack requirements: Present
Privileges required: None
User interaction: None
Confidentiality (vulnerable system): None
Integrity (vulnerable system): Low
Availability (vulnerable system): None
Confidentiality (subsequent systems): None
Integrity (subsequent systems): None
Availability (subsequent systems): None

CVSS 3.1 3.1

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

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

Weakness

CWE-285: Improper Authorization

The product does not perform or incorrectly performs an authorization check when an actor attempts to access a resource or perform an action.

How to prevent it

Architecture and Design: Divide the product into anonymous, normal, privileged, and administrative areas. Reduce the attack surface by carefully mapping roles with data and functionality. Use role-based access control (RBAC) to enforce the roles at the appropriate boundaries. Note that this approach may not protect against horizontal authorization, i.e., it will not protect a user from attacking others with the same role.
Architecture and Design: Ensure that you perform access control checks related to your business logic. These checks may be different than the access control checks that you apply to more generic resources such as files, connections, processes, memory, and database records. For example, a database may restrict access for medical records to a specific database user, but each record might only be intended to be accessible to the patient and the patient's doctor.
Architecture and Design: Use a vetted library or framework that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid. For example, consider using authorization frameworks such as the JAAS Authorization Framework [REF-233] and the OWASP ESAPI Access Control feature [REF-45].
Architecture and Design: For web applications, make sure that the access control mechanism is enforced correctly at the server side on every page. Users should not be able to access any unauthorized functionality or information by simply requesting direct access to that page. One way to do this is to ensure that all pages containing sensitive information are not cached, and that all such pages restrict access to requests that are accompanied by an active and authenticated session token associated with a user who has the required permissions to access that page.
System Configuration, Installation: Use the access control capabilities of your operating system and server environment and define your access control lists accordingly. Use a "default deny" policy when defining these ACLs.

References

Advisories

nvd.nist.gov/vuln/detail/CVE-2023-42453

Packages

github.com/matrix-org/synapse

Timeline

Sep 26, 2023 Published
Sep 10, 2026 Last updated by the source
Oct 31, 2026 Latest EPSS score

Advisory	Severity	Why it's related
GHSA-6qf2-7x63-mm6v Synapse pagination Denial of Service	Low	Also affects matrix-synapse
GHSA-8q93-326v-3m7g Synapse CPU starvation (Denial of Service)	Medium	Also affects matrix-synapse
GHSA-fh66-fcv5-jjfr Synapse's invalid device keys degrade federation functionality	Medium	Also affects matrix-synapse
GHSA-v56r-hwv5-mxg6 Synapse vulnerable to federation denial of service via malformed events	High	Also affects matrix-synapse
GHSA-56w4-5538-8v8h Synapse Matrix has a partial room state leak via Sliding Sync	Medium	Also affects matrix-synapse
GHSA-vp6v-whfm-rv3g Synapse can be forced to thumbnail unexpected file formats, invoking external, potentially untrustworthy decoders	Critical	Also affects matrix-synapse
GHSA-f3r3-h2mq-hx2h Synapse allows a a malformed invite to break the invitee's `/sync`	Medium	Also affects matrix-synapse
GHSA-rfq8-j7rh-8hf2 Synapse allows unsupported content types to lead to memory exhaustion	High	Also affects matrix-synapse

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