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🛡️ CVE-2026-45078 — matrix-synapse

🟠 CVSS 8.0 — High ✅ No Known Exploit CWE-400 NVD
8.0
CVSS Score
0 Low4 Medium7 High9 Critical10

Description

Synapse CPU starvation (Denial of Service)

Impact

Local authenticated users can cause Synapse to starve other requests of CPU and lead to other requests failing, causing other users to be denied service.

Homeservers that trust all their local users are not at risk.

Patches

Update to Synapse 1.152.1 or later.

Workarounds

If Synapse is deployed behind a reverse proxy, the reverse proxy could be configured to limit the rate of user requests,

preventing or increasing the difficulty of the attack.

Identifiers

  • ELEMENTSEC-2026-1706

For more information

If you have any questions or comments about this advisory, please email us at [security at element.io](mailto:[email protected]).

How this vulnerability can be exploited

This issue can be reached with local access to the system, attack complexity is low, an attacker needs low-level privileges on the target. No user interaction is required. The scope is unchanged, so the impact stays within the vulnerable component. Rated impact: confidentiality none, integrity none, availability high.

CVSS metrics in full

The score comes from this vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

  • Attack vector: Local — a local account, shell or session on the host is needed.
  • Attack complexity: Low — the attack works reliably, with no preparation.
  • Privileges required: Low — an ordinary user account is enough.
  • User interaction: None — nobody has to be tricked into anything.
  • Scope: Unchanged — the damage stays inside the vulnerable component.
  • Confidentiality impact: None.
  • Integrity impact: None.
  • Availability impact: High — total loss, or loss the attacker controls.

Weakness class

CVE-2026-45078 is classified as CWE-400: Uncontrolled Resource Consumption. A request can consume memory, CPU or storage without limit, exhausting capacity for everyone else.

Affected software

CVE-2026-45078 is recorded against 2 packages.

  • matrix-synapse (fixed in 1.152.1)
  • synapse (fixed in 1.152.1)

Timeline and source

Published on 14 May 2026 and last revised on 9 June 2026. No public exploit is currently recorded for this entry. Record sourced from NVD.

References

github.com (Web)
nvd.nist.gov (Advisory)
github.com (Web)
github.com (Web)
github.com (Package)
github.com (Web)

Other advisories for this package

matrix-synapse has other advisories on record. If you are patching this one, these are worth checking on the same host:

Same weakness in other software

These advisories are the same class of weakness (CWE-400: Uncontrolled Resource Consumption) in other software:

CVE-2026-45078 on other distributions

Each distribution ships its own build and its own fixed version. Pick the one you run:

Details

Severity HIGH
CVSS Score 8.0
CVSS Vector CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
CWE CWE-400
Public Exploit ✅ No
Source NVD
Published 2026-05-14
Updated 2026-08-20
Modified 2026-06-09
Fix URL N/A

Affected Packages

Software From version Fixed in
matrix-synapse — 1.152.1
synapse — 1.152.1

Site Security Check

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CVE-2026-45078 is rated CVSS 8.0 High. BotEraser scans your installation against known CVE records and tells you whether this vulnerability applies to the versions you actually run.

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ⓘ Data Notice: The information presented above has been compiled from publicly available internet sources. Boteraser aggregates this data solely for informational purposes and does not independently classify, evaluate, or endorse any findings about the vulnerabilities listed. The accuracy and completeness of this information is the sole responsibility of the original publishers. Boteraser and its operators accept no liability for any decisions made based on this data.

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