GO-2026-5067 CVE-2026-3108 GHSA-3439-vqgj-2gcf
Mattermost allows attackers to manipulate administrator terminals via crafted messages containing ANSI and OSC escape sequences in github.com/mattermost/mattermost-server
High
Go
- Severity
- 8.8 / 10
- High · CVSS 3.1
- Exploit chance (EPSS)
- 0.28%
- Chance of exploitation in the next 30 days. Higher than 20.91% of scored vulnerabilities.
- Known exploited
- No
- Not in CISA's catalog
- Weakness
- CWE-150 Improper Neutralization of Escape, Meta, or Control Sequences
- Fix
- Available
- 2 packages have a fixed version
Description
Mattermost allows attackers to manipulate administrator terminals via crafted messages containing ANSI and OSC escape sequences in github.com/mattermost/mattermost-server
Affected versions
Go
| Package | Vulnerable | Fixed in |
|---|---|---|
| github.com/mattermost/mattermost-server | >= 10.11.0-rc1+incompatible, < 10.11.11+incompatible>= 11.2.0-rc1+incompatible, < 11.2.3+incompatible>= 11.3.0-rc1+incompatible, < 11.3.2+incompatible>= 11.4.0-rc1+incompatible, < 11.4.1+incompatible |
10.11.11+incompatible11.2.3+incompatible11.3.2+incompatible11.4.1+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 | >= 11.4.0-rc1, < 11.4.1 |
11.4.1 |
| github.com/mattermost/mattermost/server/v8 | >= 11.3.0-rc1, < 11.3.2 |
11.3.2 |
| github.com/mattermost/mattermost/server/v8 | >= 11.2.0-rc1, < 11.2.3 |
11.2.3 |
| github.com/mattermost/mattermost/server/v8 | >= 10.11.0-rc1, < 10.11.11 |
10.11.11 |
| github.com/mattermost/mattermost/server/v8 | >= 8.0.0-20260105080200-d27a2195068d, < 8.0.0-20260217110922-b7d4a1f1f59b |
8.0.0-20260217110922-b7d4a1f1f59b |
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 → 11.4.1+incompatible
- go
go get github.com/mattermost/mattermost-server@v11.4.1+incompatible && go mod tidy
github.com/mattermost/mattermost/server/v8 Go → 11.4.1
- go
go get github.com/mattermost/mattermost/server/v8@v11.4.1 && go mod tidy
Severity breakdown
CVSS 3.1 8.8
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
- Attack vector
- Network
- Attack complexity
- Low
- Privileges required
- Low
- User interaction
- None
- Scope
- Unchanged
- Confidentiality
- High
- Integrity
- High
- Availability
- High
Weakness
CWE-150: Improper Neutralization of Escape, Meta, or Control Sequences
The product receives input from an upstream component, but it does not neutralize or incorrectly neutralizes special elements that could be interpreted as escape, meta, or control character sequences when they are sent to a downstream component.
How to prevent it
- Developers should anticipate that escape, meta and control characters/sequences will be injected/removed/manipulated in the input vectors of their product. Use an appropriate combination of denylists and allowlists to ensure only valid, expected and appropriate input is processed by the system.
- Implementation: Assume all input is malicious. Use an "accept known good" input validation strategy, i.e., use a list of acceptable inputs that strictly conform to specifications. Reject any input that does not strictly conform to specifications, or transform it into something that does. When performing input validation, consider all potentially relevant properties, including length, type of input, the full range of acceptable values, missing or extra inputs, syntax, consistency across related fields, and conformance to business rules. As an example of business rule logic, "boat" may be syntactically valid because it only contains alphanumeric characters, but it is not valid if the input is only expected to contain colors such as "red" or "blue." Do not rely exclusively on looking for malicious or malformed inputs. This is likely to miss at least one undesirable input, especially if the code's environment changes. This can give attackers enough room to bypass the intended validation. However, denylists can be useful for detecting potential attacks or determining which inputs are so malformed that they should be rejected outright.
- Implementation: While it is risky to use dynamically-generated query strings, code, or commands that mix control and data together, sometimes it may be unavoidable. Properly quote arguments and escape any special characters within those arguments. The most conservative approach is to escape or filter all characters that do not pass an extremely strict allowlist (such as everything that is not alphanumeric or white space). If some special characters are still needed, such as white space, wrap each argument in quotes after the escaping/filtering step. Be careful of argument injection (CWE-88).
- Implementation: Inputs should be decoded and canonicalized to the application's current internal representation before being validated (CWE-180). Make sure that the application does not decode the same input twice (CWE-174). Such errors could be used to bypass allowlist validation schemes by introducing dangerous inputs after they have been checked.
- Implementation: When using output from an LLM, neutralize or strip escape codes before redirecting output to the terminal or other rendering engine that would process the codes. The neutralization could require that the character be printable and/or allowable whitespace, such as a carriage return or newline. Be deliberate about what to allow.
- Build and Compilation: When using an LLM: during tokenizer training, suppress escape codes from the tokenizer's vocabulary. Depending on context, this could be accomplished by removing the codes from input to the tokenizer, or removing the map from the string to its token ID. It is generally unlikely that this removal would adversely affect the quality or correctness of what is generated, e.g. advice requests for terminal settings to change colors.
References
Advisories
Packages
Other links
Timeline
- Published
- Last updated by the source
- Latest EPSS score
Related advisories
| 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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