Missing request origin validation on burn-on-read reveal endpoint
Mattermost versions 11.5.x <= 11.5.1, 11.4.x <= 11.4.3 fail to validate the X-Requested-With header on the burn-on-read reveal endpoint which allows an authenticated channel member to force the reveal of a burn-on-read message without recipient consent via a crafted Markdown image tag.. Mattermost Advisory ID: MMSA-2026-00636
Noroxi analysis
No Noroxi analysis for this record yet
We don't hand-write analysis for the hundreds of thousands of vulnerabilities in the database; that wouldn't be honest. For notable, high-impact vulnerabilities our team writes the mechanism, detection and remediation steps.
We use this product, ask for help- Published
- May 18, 2026
- Updated
- Jun 17, 2026
- EPSS
- 0.2% · 4th percentile
- CWE
- CWE-346
Sign in to follow · You’ll be notified if a followed record enters KEV, gets an exploit or is updated.
Report tools
Action score
17
Monitor
Low priority for now.
- CVSS
- 17 / 40 · 4.3 / 10
- CISA KEV
- 0 / 30 · Not listed
- EPSS
- 0 / 30 · 0.2%
CISA SSVC decision
- Exploitation
- none
- Automatable
- no
- Technical impact
- partial
Vulnrichment: CISA's decision-tree inputs.
CNA vs NVD score
- NVD
- 4.3
- CNA · Mattermost
- 4.3
- agree
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L
The score given by the assigning authority versus NVD’s independent score. A gap means the severity is contested.
Affected systems
| Vendor | Product | CPE |
|---|---|---|
| mattermost | mattermost server | cpe:2.3:a:mattermost:mattermost_server |
Affected versions
NVD version ranges (for catalog products). Add the product to your stack with a version and matching uses these.
- mattermost mattermost server11.4.0 and later · before 11.4.4
- mattermost mattermost server11.5.0 and later · before 11.5.2
Versions reported by the vendor
Affected version ranges reported by the assigning authority (Mattermost). Independent of NVD's CPE analysis and usually ahead of it.
Mattermost Mattermost
- 11.6.0, 11.5.2, 11.4.4not affected
- 11.5.0 and later · up to and including 11.5.1affected · semver
- 11.4.0 and later · up to and including 11.4.3affected · semver
Package-level exposure
OSV and GitHub Advisory data: ecosystem, package and range. SBOM matching uses this table.
| Ecosystem | Package | Affected range | Fix |
|---|---|---|---|
| Go | github.com/mattermost/mattermost-server | from 11.4.0+incompatible · before 11.4.4+incompatible | 11.4.4+incompatible |
| Go | github.com/mattermost/mattermost-server | from 11.5.0+incompatible · before 11.5.2+incompatible | 11.5.2+incompatible |
| Go | github.com/mattermost/mattermost-server | before 5.3.2-0.20260327001745-7a339a6438f5 | 5.3.2-0.20260327001745-7a339a6438f5 |
| Go | github.com/mattermost/mattermost-server/v5 | all versions | — |
| Go | github.com/mattermost/mattermost-server/v6 | all versions | — |
| Go | github.com/mattermost/mattermost/server/v8 | from 11.4.0 · before 11.4.4 | 11.4.4 |
| Go | github.com/mattermost/mattermost/server/v8 | from 11.5.0 · before 11.5.2 | 11.5.2 |
| Go | github.com/mattermost/mattermost/server/v8 | before 8.0.0-20260327001745-7a339a6438f5 | 8.0.0-20260327001745-7a339a6438f5 |
Same product
mattermost: all recordsOther highest-scoring records for the same primary product.
- CVE-2026-4858Path traversal in integration action URL leading to arbitrary API execution via system admin’s auth token.39Monitor
- CVE-2025-12421Account Takeover via Code Exchange Endpoint39Monitor
- CVE-2025-12419Account takeover on OAuth/OpenID-enabled servers39Monitor
- CVE-2025-4981Path Traversal Leading to RCE by Any Authenticated Mattermost User39Monitor
- CVE-2023-6458Client side path traversal due to lack of route parameters validation39Monitor
- CVE-2017-18920An issue was discovered in Mattermost Server before 3.6.2.39Monitor
Remediation
Which version to upgrade to
Fix versions compiled from the vendor, package registries and Microsoft. Verify the vendor's note before upgrading.
| Product / package | Fixed version | Source |
|---|---|---|
| Go:github.com/mattermost/mattermost-server | 11.4.4+incompatible | Package registry (OSV) |
| Go:github.com/mattermost/mattermost-server | 11.5.2+incompatible | Package registry (OSV) |
| Go:github.com/mattermost/mattermost-server | 5.3.2-0.20260327001745-7a339a6438f5 | Package registry (OSV) |
| Go:github.com/mattermost/mattermost/server/v8 | 11.4.4 | Package registry (OSV) |
| Go:github.com/mattermost/mattermost/server/v8 | 11.5.2 | Package registry (OSV) |
| Go:github.com/mattermost/mattermost/server/v8 | 8.0.0-20260327001745-7a339a6438f5 | Package registry (OSV) |
Exploit status
No known public exploit
No public exploit has been observed yet. That doesn't mean you're safe, only that the bar is a little higher.
Research context
For pentesters and researchers: attack profile, score disagreement, timeline, patch commits, credits, variant and chain candidates, bug bounty scope. All derived from existing data; no exploit code.
Timeline
From publication to today: proof of concept, Metasploit module, CISA KEV and fix record. Dates are as reported by the sources.
No dated events beyond publication.
FIRST EPSS daily score; only changes of 0.01 or more are recorded (step chart).
Patch and commit links
Commit, PR and diff links among the references. A starting point for patch-diffing and variant hunting; fixes, not exploits.
No commit or PR link among the references.
Credits
All researchersFinders, reporters and analysts named in the CNA record. Click a name for that researcher’s other records.
- game0v3rfinder
Variant candidates
Same product, same weakness class, within 18 months. If the patch missed the root cause, the sibling bug is here.
- CVE-2026-245763 days apartWebSocket Message Spoofing via Permalink Embed Manipulation17Monitor
Chain candidates
An authentication bypass and a privilege-requiring bug in the same product, published close together: combined they may become an unauthenticated path.
—
Bug bounty scope
The product’s vendor appears in a public program. Matched by name; verify the scope text in the program.
Technical details
Attack conditions
- Anyone who can reach it over the internet can trigger it.
- A low-privileged account is enough.
- No user action is required.
- No special conditions are required; it is repeatable.
If successful
- Confidentiality
- low · data can be read
- Integrity
- none
- Availability
- none
- Attack vector
- Network
- Attack complexity
- Low
- Privileges required
- Low
- User interaction
- None
- Scope
- Unchanged
- Confidentiality impact
- Low
- Integrity impact
- None
- Availability impact
- None
Weakness class (CWE)
CWE-346 · Origin Validation ErrorCVSS vector
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N
nvd-primary
Attack context
MITRE CAPEC attack patterns and ATT&CK techniques for this weakness class (CWE). A starting point for detection rules and threat hunting.
Attack patterns (CAPEC)
- JSON Hijacking (aka JavaScript Hijacking)CAPEC-111likelihood: High · High
- Cache PoisoningCAPEC-141likelihood: High · High
- DNS Cache PoisoningCAPEC-142likelihood: High · High
- Exploit Script-Based APIsCAPEC-160Medium
- Exploitation of Trusted IdentifiersCAPEC-21likelihood: High · High
- Application API Message Manipulation via Man-in-the-MiddleCAPEC-384Low
- Transaction or Event Tampering via Application API ManipulationCAPEC-385Medium
- Application API Navigation RemappingCAPEC-386Medium
ATT&CK techniques
- Access Token ManipulationT1134
- Access Token Manipulation:Token Impersonation/TheftT1134.001
- Steal Application Access TokenT1528
- Steal Web Session CookieT1539
- Use Alternate Authentication Material:Web Session CookieT1550.004
- Adversary-in-the-Middle: ARP Cache PoisoningT1557.002
- Compromise Infrastructure: DNS ServerT1584.002
Change log
- Fix✗ → ✓
For records you follow, these changes also arrive as notifications. →
References
Vendor advisories and official records. Exploit/PoC links are deliberately left out.