CVE-2023-42453 | Improper validation of receipts allows forged read receipts in matrix synapse

Synapse is an open-source Matrix homeserver written and maintained by the Matrix.org Foundation. 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. This issue has been patched in version 1.93.0. Users are advised to upgrade. There are no known workarounds for this issue.

Published: 2023-09-27 Last update: 2024-11-21 Assigner: [email protected] Source: [email protected]
NVD Status：Modified，CVE State: published
View at NVD, CVE.org, EUVD

CVE-2023-42453 is rated Low Risk (23.6/100): CVSS Low severity, with low exploitation likelihood (EPSS 0.13%). Monitor for updates and reassess as exploit intelligence or EPSS changes.

Risk is dynamic; we continuously reassess and refresh what is shown on this page as upstream context changes.

Exploit prediction scoring system (EPSS) score for CVE-2023-42453

EPSS lead: Daily EPSS estimates relative likelihood of exploitation; percentile ranks this CVE among scored vulnerabilities (higher = more severe relative rank).

# Date Old EPSS score New EPSS score Delta (New - Old)
1 2026-06-01 0.22% 0.13% -0.09%
2 2025-11-21 0.31% 0.22% -0.09%
3 2025-11-18 — 0.31% —

Full EPSS history (10 records total)

Common vulnerability scoring system (CVSS) metrics for CVE-2023-42453

CVSS metrics for this CVE.

Base score Version Severity Vector Exploitability Impact Score source
3.1 3.1 LOW
CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:N/I:L/A:N Click to expand
Attack vector (AV:N)
Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
Attack complexity (AC:H)
Even with access, the exploit needs extra luck, timing, or a fussy environment to actually work.
Privileges required (PR:L)
A normal user session is enough; they don’t have to be admin.
User interaction (UI:N)
Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:U)
Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:N)
Doesn’t really leak secrets in a meaningful way.
Integrity (I:L)
Attackers could change some data, but it’s limited—not everything goes.
Availability (A:N)
Service keeps running; no real outage angle.
 1.6 1.4 [email protected]
4.3 3.1 MEDIUM
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:L/A:N Click to expand
Attack vector (AV:N)
Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
Attack complexity (AC:L)
Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
Privileges required (PR:L)
A normal user session is enough; they don’t have to be admin.
User interaction (UI:N)
Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:U)
Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:N)
Doesn’t really leak secrets in a meaningful way.
Integrity (I:L)
Attackers could change some data, but it’s limited—not everything goes.
Availability (A:N)
Service keeps running; no real outage angle.
 2.8 1.4 [email protected]

Weakness enumeration for CVE-2023-42453

GitHub Security Advisory for CVE-2023-42453

GHSA-7565-cq32-vx2x · Severity: medium · Ecosystem: pip — matrix-synapse vulnerable to improper validation of receipts allows forged read receipts

OS Trackers for CVE-2023-42453

vendor priority summary link
alpine — CVE-2023-42453: 1 source package rows (synapse); 20 state rows across 6 repos (3.18-community, 3.19-community, 3.20-community, 3.21-community, 3.22-community, edge-community); fixed 6, open 14. https://security.alpinelinux.org/vuln/CVE-2023-42453
debian not yet assigned CVE-2023-42453 not yet assigned priority: Debian including 1 source packages (matrix-synapse), 2 status rows across 2 suites (forky, sid): resolved 2. https://security-tracker.debian.org/tracker/CVE-2023-42453
gentoo low CVE-2023-42453: 1 GLSA(s) (202401-12), 1 atom(s) (net-im/synapse); latest impact low. https://bugs.gentoo.org/buglist.cgi?quicksearch=CVE-2023-42453
ubuntu medium CVE-2023-42453 medium priority: Ubuntu including 1 source packages (matrix-synapse), 10 status rows across 10 suites (bionic, focal, jammy, lunar, mantic, noble, oracular, trusty, upstream, xenial): ignored 6, not-affected 2, released 2. https://ubuntu.com/security/CVE-2023-42453

Affected software / configurations for CVE-2023-42453

Vendor Product Version Raw CPE
matrix synapse >= 1.34.0, < 1.93.0 cpe:2.3:a:matrix:synapse:*:*:*:*:*:*:*:*
fedoraproject fedora 37 cpe:2.3:o:fedoraproject:fedora:37:*:*:*:*:*:*:*
fedoraproject fedora 38 cpe:2.3:o:fedoraproject:fedora:38:*:*:*:*:*:*:*

References for CVE-2023-42453

cvelogic Threat Intelligence