Channel client denial of service via regex backtracking
Published Jul 13, 2026 · Updated Jul 13, 2026
ReDoS in affected Mattermost releases allows remote authenticated users to interrupt channel clients via crafted attachment fields. The server accepts attacker-controlled attachment field values whose length and content cause catastrophic backtracking in the client-side markdown parser. Authentication and channel posting access are required; the crafted post disrupts every client rendering that channel without changing server data.
Summary
What happened
ReDoS in affected Mattermost releases allows remote authenticated users to interrupt channel clients via crafted attachment fields. The server accepts attacker-controlled attachment field values whose length and content cause catastrophic backtracking in the client-side markdown parser. Authentication and channel posting access are required; the crafted post disrupts every client rendering that channel without changing server data.
The record
- CVE
- CVE-2026-6850
- Published
- Jul 13, 2026
- Updated
- Jul 13, 2026
- Vendor
- Mattermost
- Product
- Mattermost
- Classifications
- CWE-1333, T1499.004
- Attack vector
- network
- Privileges
- authenticated
Timeline
How it unfolded
- Jul 13, 2026CVE publishedPublication date reported by the CVE source.
- Jul 13, 2026Record updatedLatest update available in the CVE record.
Exploitability
Present is not the same as exploitable
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Is a vulnerable build present?
Compare these published version ranges with your installed build and any vendor patches.
- Affected versionversion=10.11.0 <=10.11.19
- Affected versionversion=11.6.0 <=11.6.4
- Affected versionversion=11.7.0 <=11.7.2
What conditions does exploitation require?
What is affected?
Published CVSS scores
CVSS describes severity. EPSS estimates exploitation probability.
Attacks
What attackers are doing with it
Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.
Weakness, pattern, technique
Public exploit references
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Technologies
Your stack
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Your stack
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