Mattermost <1.12 DoS via oversized zlibcompressed SDP messages (v10.1111.9)
CVE-2026-5132 Published on September 14, 2026

Unbounded zlib decompression in Calls SDP WebSocket messages
Mattermost versions 11.9.x <= 11.9.0, 11.8.x <= 11.8.4, 11.7.x <= 11.7.7, 10.11.x <= 10.11.22 fail to limit size of unpacked SDP messages compressed with zlib, which allows attacker to deny service or crash server via sending many SDP messages that unpack to large size.. Mattermost Advisory ID: MMSA-2026-00643

Vendor Advisory NVD

Vulnerability Analysis

CVE-2026-5132 is exploitable with network access, and requires small amount of user privileges. This vulnerability is considered to have a low attack complexity. The potential impact of an exploit of this vulnerability is considered to have no impact on confidentiality and integrity, and a high impact on availability.

Attack Vector:
NETWORK
Attack Complexity:
LOW
Privileges Required:
LOW
User Interaction:
NONE
Scope:
UNCHANGED
Confidentiality Impact:
NONE
Integrity Impact:
NONE
Availability Impact:
HIGH

Weakness Type

What is a Data Amplification Vulnerability?

The software does not handle or incorrectly handles a compressed input with a very high compression ratio that produces a large output. An example of data amplification is a "decompression bomb," a small ZIP file that can produce a large amount of data when it is decompressed.

CVE-2026-5132 has been classified to as a Data Amplification vulnerability or weakness.


Products Associated with CVE-2026-5132

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MatterMost
 

Affected Versions

Mattermost: