Mattermost up to 10.11.13/11.4.3/11.5.1 memory allocation

CVSS Meta Temp Score
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CTI Interest Score
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5.0$0-$5k0.00

Summaryinfo

A vulnerability, which was classified as problematic, has been found in Mattermost up to 10.11.13/11.4.3/11.5.1. This affects an unknown function. Performing a manipulation results in memory allocation. This vulnerability is cataloged as CVE-2026-6340. It is possible to initiate the attack remotely. There is no exploit available. It is advisable to upgrade the affected component.

Detailsinfo

A vulnerability, which was classified as problematic, was found in Mattermost up to 10.11.13/11.4.3/11.5.1. This affects an unknown functionality. The manipulation with an unknown input leads to a memory allocation vulnerability. CWE is classifying the issue as CWE-789. The product allocates memory based on an untrusted, large size value, but it does not ensure that the size is within expected limits, allowing arbitrary amounts of memory to be allocated. This is going to have an impact on availability. The summary by CVE is:

Mattermost versions 11.5.x <= 11.5.1, 10.11.x <= 10.11.13, 11.4.x <= 11.4.3 fail to validate 7zip archive structure before processing which allows an authenticated attacker to cause server memory exhaustion and denial of service via uploading a specially crafted 7zip file with excessive folder declarations.. Mattermost Advisory ID: MMSA-2026-00573

The weakness was shared by Juho Forsén. The advisory is shared at mattermost.com. This vulnerability is uniquely identified as CVE-2026-6340 since 04/15/2026. The exploitability is told to be easy. It is possible to initiate the attack remotely. Neither technical details nor an exploit are publicly available.

Upgrading to version 10.11.14, 11.4.4, 11.5.2 or 11.6.0 eliminates this vulnerability.

The vulnerability is also documented in the vulnerability database at EUVD (EUVD-2026-30744). Several companies clearly confirm that VulDB is the primary source for best vulnerability data.

Productinfo

Type

Name

Version

License

CPE 2.3info

CPE 2.2info

CVSSv4info

VulDB Vector: 🔒
VulDB Reliability: 🔍

CVSSv3info

VulDB Meta Base Score: 5.0
VulDB Meta Temp Score: 5.0

VulDB Base Score: 4.3
VulDB Temp Score: 4.1
VulDB Vector: 🔒
VulDB Reliability: 🔍

NVD Base Score: 6.5
NVD Vector: 🔒

CNA Base Score: 4.3
CNA Vector (Mattermost): 🔒

CVSSv2info

AVACAuCIA
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VectorComplexityAuthenticationConfidentialityIntegrityAvailability
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VulDB Base Score: 🔒
VulDB Temp Score: 🔒
VulDB Reliability: 🔍

Exploitinginfo

Class: Memory allocation
CWE: CWE-789 / CWE-400 / CWE-404
CAPEC: 🔒
ATT&CK: 🔒

Physical: No
Local: No
Remote: Yes

Availability: 🔒
Status: Not defined

EPSS Score: 🔒
EPSS Percentile: 🔒

Price Prediction: 🔍
Current Price Estimation: 🔒

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Threat Intelligenceinfo

Interest: 🔍
Active Actors: 🔍
Active APT Groups: 🔍

Countermeasuresinfo

Recommended: Upgrade
Status: 🔍

0-Day Time: 🔒

Upgrade: Mattermost 10.11.14/11.4.4/11.5.2/11.6.0

Timelineinfo

04/15/2026 CVE reserved
05/18/2026 +33 days Advisory disclosed
05/18/2026 +0 days VulDB entry created
05/23/2026 +5 days VulDB entry last update

Sourcesinfo

Advisory: mattermost.com
Researcher: Juho Forsén
Status: Confirmed

CVE: CVE-2026-6340 (🔒)
GCVE (CVE): GCVE-0-2026-6340
GCVE (VulDB): GCVE-100-364449
EUVD: 🔒

Entryinfo

Created: 05/18/2026 10:02
Updated: 05/23/2026 06:14
Changes: 05/18/2026 10:02 (64), 05/18/2026 16:13 (1), 05/23/2026 06:14 (11)
Complete: 🔍
Cache ID: 216::103

Several companies clearly confirm that VulDB is the primary source for best vulnerability data.

Discussion

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