GHSA-9p92-x77w-9fw2 CVE-2025-9078 GO-2025-3959

Mattermost makes Use of Weak Hash

Medium Go

Severity: 4.3 / 10; Medium · CVSS 3.1
Exploit chance (EPSS): 0.15%; Chance of exploitation in the next 30 days. Higher than 4.53% of scored vulnerabilities.
Known exploited: No; Not in CISA's catalog
Weakness: CWE-328 Use of Weak Hash
Fix: Available; 2 packages have a fixed version

Description

Mattermost versions 10.8.x <= 10.8.3, 10.5.x <= 10.5.8, 9.11.x <= 9.11.17, 10.10.x <= 10.10.1, 10.9.x <= 10.9.3 fail to properly validate cache keys for link metadata which allows authenticated users to access unauthorized posts and poison link previews via hash collision attacks on FNV-1 hashing.

Affected versions

Go

Package	Vulnerable	Fixed in
github.com/mattermost/mattermost-server	`>= 10.8.0, < 10.8.4`	`10.8.4`
github.com/mattermost/mattermost-server	`>= 10.5.0, < 10.5.9`	`10.5.9`
github.com/mattermost/mattermost-server	`>= 9.11.0, < 9.11.18`	`9.11.18`
github.com/mattermost/mattermost-server	`>= 10.10.0, < 10.10.2`	`10.10.2`
github.com/mattermost/mattermost-server	`>= 10.9.0, < 10.9.4`	`10.9.4`
github.com/mattermost/mattermost-server	`>= 9.11.0+incompatible, < 9.11.18+incompatible` `>= 10.5.0+incompatible, < 10.5.9+incompatible` `>= 10.8.0+incompatible, < 10.8.4+incompatible` `>= 10.9.0+incompatible, < 10.9.4+incompatible` `>= 10.10.0+incompatible, < 10.10.2+incompatible`	`9.11.18+incompatible` `10.5.9+incompatible` `10.8.4+incompatible` `10.9.4+incompatible` `10.10.2+incompatible`
github.com/mattermost/mattermost-server/v5	`all versions`	No fix yet
github.com/mattermost/mattermost-server/v6	`all versions`	No fix yet
github.com/mattermost/mattermost/server/v8	`< 8.0.0-20250718075842-cd87e5c87737`	`8.0.0-20250718075842-cd87e5c87737`

How to fix

Move to the fixed version or later with your package manager, update the lockfile, and run your tests. If the package only arrives through another dependency, upgrade that dependency first. If none of its releases pulls a fixed version yet, force the version with your package manager's override.

github.com/mattermost/mattermost-server Go → `10.8.4`

go

go get github.com/mattermost/mattermost-server@v10.8.4 && go mod tidy

github.com/mattermost/mattermost/server/v8 Go → `8.0.0-20250718075842-cd87e5c87737`

go

go get github.com/mattermost/mattermost/server/v8@v8.0.0-20250718075842-cd87e5c87737 && go mod tidy

Severity breakdown

CVSS 3.1 4.3

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

Attack vector: Network
Attack complexity: Low
Privileges required: Low
User interaction: None
Scope: Unchanged
Confidentiality: Low
Integrity: None
Availability: None

Weakness

CWE-328: Use of Weak Hash

The product uses an algorithm that produces a digest (output value) that does not meet security expectations for a hash function that allows an adversary to reasonably determine the original input (preimage attack), find another input that can produce the same hash (2nd preimage attack), or find multiple inputs that evaluate to the same hash (birthday attack).

How to prevent it

Architecture and Design: Use an adaptive hash function that can be configured to change the amount of computational effort needed to compute the hash, such as the number of iterations ("stretching") or the amount of memory required. Some hash functions perform salting automatically. These functions can significantly increase the overhead for a brute force attack compared to intentionally-fast functions such as MD5. For example, rainbow table attacks can become infeasible due to the high computing overhead. Finally, since computing power gets faster and cheaper over time, the technique can be reconfigured to increase the workload without forcing an entire replacement of the algorithm in use. Some hash functions that have one or more of these desired properties include bcrypt [REF-291], scrypt [REF-292], and PBKDF2 [REF-293]. While there is active debate about which of these is the most effective, they are all stronger than using salts with hash functions with very little computing overhead. Note that using these functions can have an impact on performance, so they require special consideration to avoid denial-of-service attacks. However, their configurability provides finer control over how much CPU and memory is used, so it could be adjusted to suit the environment's needs.

References

Advisories

Packages

github.com/mattermost/mattermost

Timeline

Sep 15, 2025 Published
Oct 19, 2026 Last updated by the source
Oct 31, 2026 Latest EPSS score

Advisory	Severity	Why it's related
GHSA-xmfh-3ccg-c9fx Mattermost has an Incorrect Authorization issue	Low	Also affects github.com/mattermost/mattermost-server
GHSA-h998-hxxj-8q83 Mattermost doesn't invalidate cached authentication state for active WebSocket connections during global session revocation	Medium	Also affects github.com/mattermost/mattermost-server
GHSA-g5vr-6pgg-74qv Mattermost doesn't enforce bot-specific permission checks on the user active status endpoint	Low	Also affects github.com/mattermost/mattermost-server
GHSA-jqgv-39mg-7c2r Mattermost doesn't authenticate Atlassian Connect installed callbacks, allowing a remote unauthenticated attacker to inject a rogue sharedSecret	Medium	Also affects github.com/mattermost/mattermost-server
GHSA-mxq2-5jpg-7474 Mattermost doesn't validate channel ownership of an existing subscription before applying edits	Medium	Also affects github.com/mattermost/mattermost-server
GHSA-2g8v-grq3-hq2g Mattermost doesn't enforce administrator authorization on the {{setDefaultInstance}} call within the {{/gitlab connect}} command handler	Medium	Also affects github.com/mattermost/mattermost-server
GHSA-6hxm-w4hv-vgvw Mattermost doesn't require role-management authorization when setting the scheme_admin flag on group syncable link and patch endpoints	High	Also affects github.com/mattermost/mattermost-server
GHSA-9p44-r552-4wp9 Mattermost doesn't sanitize the Remote Cluster API response on PATCH operations	Medium	Also affects github.com/mattermost/mattermost-server

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