How severe is CVE-2023-40703?

CVE-2023-40703 has a CVSS score of 4.3/10, rated MEDIUM. Review your exposure and patch according to your risk tolerance.

Which packages are affected by CVE-2023-40703?

CVE-2023-40703 affects the following packages: github.com/mattermost/mattermost/server/v8 (Go), github.com/mattermost/mattermost/server/v8 (Go), github.com/mattermost/mattermost/server/v8 (Go), github.com/mattermost/mattermost-server/v6 (Go). Ecosystems affected: Go.

How do I fix CVE-2023-40703?

Update github.com/mattermost/mattermost/server/v8 to 9.1.1 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2023-40703 is resolved across your whole dependency graph.

How do I detect CVE-2023-40703 in my Go dependencies?

Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for github.com/mattermost/mattermost/server/v8. O3's reachability analysis confirms whether the vulnerable code path is actually invoked in your application, so you act on real exposure instead of every transitive match.

How do I mitigate CVE-2023-40703 if there is no patch (or I can't update yet)?

If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.

How does O3 Security protect against CVE-2023-40703?

O3 pinpoints whether CVE-2023-40703 is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.

Is CVE-2023-40703 actively exploited in the wild?

No public exploit code has been indexed for CVE-2023-40703 yet. This does not mean the vulnerability cannot be exploited — absence of public exploits does not imply safety. Apply the recommended fix and use O3 Security to monitor your exposure.

What type of vulnerability is CVE-2023-40703?

CVE-2023-40703 is classified as Uncontrolled Resource Consumption (CWE-400). This weakness type describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation.

When was CVE-2023-40703 published, and has it been updated?

CVE-2023-40703 was published on November 27, 2023 and was last updated on July 15, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

🐹 Go

CVE-2023-40703

MEDIUM

CVE-2023-40703 is a medium-severity (CVSS 4.3) Uncontrolled Resource Consumption vulnerability in github.com/mattermost/mattermost/server/v8. O3 Security confirms whether CVE-2023-40703 is actually reachable in your code before you act, and blocks exploitation at runtime until you patch.

Denial of Service via specially crafted block fields in Mattermost Boards

Also known asGHSA-c37r-v8jx-7cv2

Published

Nov 27, 2023

Updated

Jul 15, 2026

Affected

4 pkgs

Patched

4 / 4

Exploits

None indexed

Blast Radius

4 pkgs affected

🐹github.com/mattermost/mattermost/server/v8🐹github.com/mattermost/mattermost/server/v8🐹github.com/mattermost/mattermost/server/v8🐹github.com/mattermost/mattermost-server/v6

Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects Go packages — download data is not available via public APIs for these ecosystems.

Description

Mattermost fails to properly limit the characters allowed in different fields of a block in Mattermost Boards allowing a attacker to consume excessive resources, possibly leading to Denial of Service, by patching the field of a block using a specially crafted string.

Affected Packages

4 total 4 fixed

Ecosystem	Package	Vulnerable range	Fix
🐹Go	`github.com/mattermost/mattermost/server/v8`	≥ 9.1.0&&< 9.1.1	9.1.1
🐹Go	`github.com/mattermost/mattermost/server/v8`	≥ 9.0.0&&< 9.0.2	9.0.2
🐹Go	`github.com/mattermost/mattermost/server/v8`	all versions	8.1.4
🐹Go	`github.com/mattermost/mattermost-server/v6`	all versions	7.8.13

Detection & mitigation playbook

Open-source dependency

Detect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for github.com/mattermost/mattermost/server/v8. O3's reachability analysis confirms whether the vulnerable code path is actually invoked in your application, so you act on real exposure instead of every transitive match.
Fix
Update github.com/mattermost/mattermost/server/v8 to 9.1.1 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2023-40703 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 pinpoints whether CVE-2023-40703 is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.

Tailored to CVE-2023-40703. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.

Frequently Asked Questions

O3 Security · Impact-Aware SCA

Is CVE-2023-40703 in your dependencies?

O3 detects CVE-2023-40703 across Go dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.

Scan my dependencies How O3 SCA works