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Fencer Vulns
low 3.1

CVE-2023-42453 json

Improper validation of receipts allows forged read receipts in matrix synapse

published 2023-09-26 3 y ago modified 2026-09-10 1 mo ago also GHSA-7565-cq32-vx2x , PYSEC-2023-180 , EUVD-2023-0133

cvss
3.1
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.8%
EPSS 0.8% chance of exploitation in 30 days, percentile 56%
public exploits
0
none known

Summary

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.

Patch / fix

  • pypi matrix-synapse 1.93.0
  • matrix synapse 1.93.0
  • matrix-synapse Ubuntu Pro 22.04 LTS 1.53.0-1ubuntu0.1~esm2

ubuntu advisories UBUNTU-CVE-2023-42453

Ubuntu security data © Canonical Ltd., from https://github.com/canonical/ubuntu-security-notices via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

  • matrix-synapse openSUSE Tumbleweed 1.93.0-1.1

opensuse advisories openSUSE-SU-2024:13270-1

  • synapse Alpine 3.24, Alpine 3.23, Alpine 3.22 +4 more 1.93.0-r0

alpine advisories ALPINE-CVE-2023-42453

Alpine secdb © Alpine Linux, from https://secdb.alpinelinux.org via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2023-42453 updated cvss 4.3

matrix-synapse: improper validation of receipts allows forged read receipts

  • Red Hat All currently supported Red Hat products
    not affected: vulnerable code not present

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

CISA SSVC

Exploitation
none
Automatable
no
Technical impact
partial
Assessed
2 y ago

Exploit prediction

0.78% chance of exploitation in the next 30 days, higher than 56% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
CNA 3.1 3.1 CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:N/I:L/A:N
NVD 3.1 4.3 CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:L/A:N
GitHub 3.1 3.1 CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:N/I:L/A:N
OSV 3.1 4.3 CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:L/A:N

Affected packages

ecosystem package affected fixed in
pypi matrix-synapse
>=0.34.0, <1.93.0
>=1.34.0, <1.93.0
1.93.0

Affected products

  • matrix-org synapse

Classification

Weakness

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.