PYSEC-2026-846

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    PYSEC-2026-846

    Published: 6 Jul 2026Last Modified: 7 Jul 2026

    Summary: Matrix Synapse DoS

    Details: Matrix Synapse before 0.28.1 is prone to a denial of service flaw where malicious events injected with depth = 2<sup>63</sup> - 1 render rooms unusable, related to `federation/federation_base.py` and `handlers/message.py`, as exploited in the wild in April 2018.

    References: https://nvd.nist.gov/vuln/detail/CVE-2018-10657, https://github.com/matrix-org/synapse/commit/33f469ba19586bbafa0cf2c7d7c35463bdab87eb, https://docs.google.com/document/d/1I3fi2S-XnpO45qrpCsowZv8P8dHcNZ4fsBsbOW7KABI/edit#heading=h.fj95ykuss7s1, https://github.com/matrix-org/synapse, https://matrix.org/blog/2018/05/01/security-update-synapse-0-28-1, https://pypi.org/project/matrix-synapse, https://github.com/advisories/GHSA-vmcc-4p4x-x7wg

    Affected packages

    Package

    Name: matrix-synapse

    Purl: pkg:pypi/matrix-synapse

    Affected ranges

    Type: ECOSYSTEM

    Events:

    Introduced- 0
    Fixed -0.28.1

    Affected versions

    Common Vulnerability Scoring System

    Attack Vector
    Network
    Adjacent
    Local
    Physical
    Privileges Required
    None
    Low
    High
    User Interaction
    None
    Required
    Scope
    Unchanged
    Changed
    Confidentiality
    None
    Low
    High
    Integrity
    None
    Low
    High
    Availability
    None
    Low
    High
    PYSEC-2026-846 | CVE-DB