CVE-2026-2456
Mattermost Server 10.11.0 – 10.11.11
Raw vector
CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:N/I:N/A:HSummary
CVE-2026-2456 is a medium-severity Memory Allocation with Excessive Size Value (CWE-789) vulnerability in Mattermost Mattermost Server. Its CVSS base score is 5.3 (Medium).
Operationally, exploitation aligns with the MITRE ATT&CK technique Application Exhaustion Flood (T1499.003); ranked at the 6th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog.
The strongest mitigations our analysis identified map to SC-5 (Denial-of-service Protection) and SI-10 (Information Input Validation) — see the control section below for these in your framework.
EU & UK References
- 🇪🇺 ENISA EUVD: EUVD-2026-12383
Vulnerability Data
Mattermost versions 11.3.x <= 11.3.0, 11.2.x <= 11.2.2, 10.11.x <= 10.11.10 Mattermost fails to limit the size of responses from integration action endpoints, which allows an authenticated attacker to cause server memory exhaustion and denial of service via a malicious…
more
integration server that returns an arbitrarily large response when a user clicks an interactive message button.. Mattermost Advisory ID: MMSA-2026-00571
- CWE(s)
Related Threats
MITRE ATT&CK Enterprise TechniquesAI
Why these techniques?
Unbounded response size from integration endpoints directly enables application memory exhaustion DoS (T1499.003/004).
CVEs Like This One
Affected Assets
Mitigating Controls
Control response
Mitigating Controls (NIST 800-53 r5) AI
Directly requires validation of input size and format, which would have rejected the arbitrarily large responses from the malicious integration endpoint before memory allocation.
Mandates denial-of-service protection mechanisms such as resource quotas and traffic throttling that would limit memory exhaustion from oversized integration responses.
Enables monitoring of system resource consumption and anomalous network responses, allowing detection of the large payloads causing memory exhaustion.
Mitigating Controls (NIST CSF 2.0) AI
Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→CSF cross-walk (authority under review) — links open the control.
Secure SDLC practices directly prevent coding flaws that trust unvalidated size values for allocations.
Mitigating Controls (ISO/IEC 27001:2022 Annex A) AI
Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→ISO cross-walk (authority under review) — links open the control.
Security testing in development can detect and block excessive allocation flaws before deployment.
Secure development lifecycle includes input validation and size checks that prevent unbounded allocations.
Application security requirements mandate bounds checking on size parameters to avoid excessive memory allocation.
Secure architecture principles require resource-limit enforcement that mitigates uncontrolled memory requests.
Secure coding standards directly prohibit allocating memory from untrusted size values without validation.
Capacity management monitors overall resource use but does not prevent individual allocation bugs.