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CVE-2026-2455· NVD / CVE Program· CNA Mattermost

SSRF bypass via IPv4-mapped IPv6 literals

Mattermost versions 11.3.x <= 11.3.0, 11.2.x <= 11.2.2, 10.11.x <= 10.11.10 fail to canonicalize IPv4-mapped IPv6 addresses before reserved IP validation which allows an attacker to perform SSRF attacks against internal services via IPv4-mapped IPv6 literals (e.g., [::ffff:127.0.0.1]).. Mattermost Advisory ID: MMSA-2026-00585

MediumCVSS 4.3 · v3.1—No exploit Fix available

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Published
Mar 16, 2026
Updated
Jun 17, 2026
EPSS
0.2% · 5th percentile
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Report tools

JSON

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
—
CNA · Mattermost
4.3
NVD has not scored this yet; the score shown is the CNA’s.

The score given by the assigning authority versus NVD’s independent score. A gap means the severity is contested.

Affected systems

VendorProduct
mattermostmattermost server

Affected versions

NVD version ranges (for catalog products). Add the product to your stack with a version and matching uses these.

  • mattermost mattermost server10.11.0 and later · before 10.11.11
  • mattermost mattermost server11.2.0 and later · before 11.2.3
  • mattermost mattermost server11.3.0 and later · before 11.3.1

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

    • 11.4.0, 11.3.1, 11.2.3, 10.11.11not affected
    • 11.3.0 and later · up to and including 11.3.0affected · semver
    • 11.2.0 and later · up to and including 11.2.2affected · semver
    • 10.11.0 and later · up to and including 10.11.10affected · semver

Package-level exposure

OSV and GitHub Advisory data: ecosystem, package and range. SBOM matching uses this table.

EcosystemPackageAffected rangeFix
Gogithub.com/mattermost/mattermost-serverfrom 10.11.0-rc1 · before 10.11.1110.11.11
Gogithub.com/mattermost/mattermost-serverfrom 10.11.0-rc1+incompatible · before 10.11.11+incompatible10.11.11+incompatible
Gogithub.com/mattermost/mattermost-serverfrom 11.2.0-rc1 · before 11.2.311.2.3
Gogithub.com/mattermost/mattermost-serverfrom 11.2.0-rc1+incompatible · before 11.2.3+incompatible11.2.3+incompatible
Gogithub.com/mattermost/mattermost-serverfrom 11.3.0-rc1 · before 11.3.111.3.1
Gogithub.com/mattermost/mattermost-serverfrom 11.3.0-rc1+incompatible · before 11.3.1+incompatible11.3.1+incompatible
Gogithub.com/mattermost/mattermost-serverbefore 5.3.2-0.20260129133647-5d787969c2d55.3.2-0.20260129133647-5d787969c2d5
Gogithub.com/mattermost/mattermost-server/v5all versions—
Gogithub.com/mattermost/mattermost-server/v6all versions—
Gogithub.com/mattermost/mattermost/server/v8before 8.0.0-20260129133647-5d787969c2d58.0.0-20260129133647-5d787969c2d5
openSUSE:Leap 15.6govulncheck-vulndbbefore 0.0.20260326T203309-150000.1.155.20.0.20260326T203309-150000.1.155.2

Same product

mattermost: all records

Other 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 Endpoint
    39Monitor
  • CVE-2025-12419Account takeover on OAuth/OpenID-enabled servers
    39Monitor
  • CVE-2025-4981Path Traversal Leading to RCE by Any Authenticated Mattermost User
    39Monitor
  • CVE-2023-6458Client side path traversal due to lack of route parameters validation
    39Monitor
  • 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 / packageFixed versionSource
Go:github.com/mattermost/mattermost-server10.11.11Package registry (OSV)
Go:github.com/mattermost/mattermost-server10.11.11+incompatiblePackage registry (OSV)
Go:github.com/mattermost/mattermost-server11.2.3Package registry (OSV)
Go:github.com/mattermost/mattermost-server11.2.3+incompatiblePackage registry (OSV)
Go:github.com/mattermost/mattermost-server11.3.1Package registry (OSV)
Go:github.com/mattermost/mattermost-server11.3.1+incompatiblePackage registry (OSV)
Go:github.com/mattermost/mattermost-server5.3.2-0.20260129133647-5d787969c2d5Package registry (OSV)
Go:github.com/mattermost/mattermost/server/v88.0.0-20260129133647-5d787969c2d5Package registry (OSV)
opensuse:govulncheck-vulndb0.0.20260326T203309-150000.1.155.2 · openSUSE:Leap 15.6Package 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.

EPSS, last 120 days

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 researchers

Finders, reporters and analysts named in the CNA record. Click a name for that researcher’s other records.

Variant candidates

Same product, same weakness class, within 18 months. If the patch missed the root cause, the sibling bug is here.

  • CVE-2026-4339102 days apartSSRF via unvalidated attachment URLs in Mattermost Agents plugin MCP server
    26Monitor
  • CVE-2024-45843536 days apartMattermost versions 9.5.x <= 9.5.8 fail to include the metadata endpoints of Oracle Cloud and Alibaba in the SSRF denylist, which allows an
    21Monitor
  • CVE-2026-633363 days apartSSRF via Host Header Spoofing in Custom Slash Commands
    20Monitor
  • CVE-2025-47700207 days apartAI plugin APIs can be triggered using post actions
    14Monitor

Chain candidates

An authentication bypass and a privilege-requiring bug in the same product, published close together: combined they may become an unauthenticated path.

  • CVE-2026-099928 days apartAuthentication bypass via userID login when email and username login are disabled
    17Monitor

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-918 · Server-Side Request Forgery (SSRF)

CVSS vector

CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N

nvd-secondary

Attack context

MITRE CAPEC attack patterns and ATT&CK techniques for this weakness class (CWE). A starting point for detection rules and threat hunting.

ATT&CK techniques

—

Change log

  1. Fix✗ → ✓

For records you follow, these changes also arrive as notifications. →

References

Vendor advisories and official records. Exploit/PoC links are deliberately left out.

All records