What is the CVSS score of CVE-2026-43888?

CVE-2026-43888 has a CVSS 3.1 base score of 8.7 (High). CVSS vector: CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:C/C:N/I:H/A:H. EPSS exploitation probability: 0.0%.

Which versions of Outline are affected by CVE-2026-43888?

Outline self-hosted knowledge base versions before 1.7.0 contain a sandbox escape vulnerability affecting authenticated users with import privileges, enabling arbitrary file writes to the server's…. A patch is available.

How to fix or mitigate CVE-2026-43888?

Within 24 hours: Identify all Outline deployments and confirm current versions. Within 7 days: Deploy Outline 1.7.0 or later to all instances, verify successful upgrades, and monitor import activity logs for suspicious behavior. Within 30 days: Audit and restrict import privileges to only essential users, and establish ongoing monitoring for import-related access patterns.

Outline CVE-2026-43888

EUVD-2026-29332 HIGH

Path Traversal (CWE-22)

2026-05-11 GitHub_M

Path Traversal Outline

8.7

CVSS 3.1 · GitHub Advisory

Severity by source

GitHub Advisory PRIMARY

8.7 HIGH

AV:N/AC:L/PR:H/UI:N/S:C/C:N/I:H/A:H

vuln.today AI

8.5 HIGH

Import is typically available to authenticated members so PR:L (vendor used PR:H); sandbox escape justifies S:C, arbitrary-filename write gives I:H, C:N, and A:L since only working-dir files may be clobbered.

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

4.0 AV:N/AC:L/AT:N/PR:L/UI:N/VC:N/VI:H/VA:L/SC:N/SI:N/SA:N

Primary rating from GitHub Advisory.

CVSS VectorGitHub Advisory

Attack Vector

Network

Attack Complexity

Low

Privileges Required

High

User Interaction

None

Scope

Changed

Confidentiality

None

Integrity

High

Availability

High

Lifecycle Timeline

Analysis Generated

Jul 23, 2026 - 23:32 vuln.today

Patch available

May 11, 2026 - 23:03 EUVD

CVE Published

May 11, 2026 - 21:09 nvd

HIGH 8.7

DescriptionGitHub Advisory

Outline is a service that allows for collaborative documentation. Prior to 1.7.0, ZipHelper.extract computes the extraction path for each entry by passing a full filesystem path through trimFileAndExt, a filename helper that calls path.basename on its input when truncating. When a zip entry's nested path is long enough to push the joined filesystem path over MAX_PATH_LENGTH (4096 bytes), trimFileAndExt silently drops all directory components and returns a bare filename. fs.createWriteStream then opens the file relative to the process working directory instead of inside the extraction sandbox, and the escaped file persists after import cleanup because cleanupExtractedData only removes the temporary extraction directory. This vulnerability is fixed in 1.7.0.

AnalysisAI

Zip extraction sandbox escape in Outline (self-hosted collaborative knowledge base) before 1.7.0 lets an authenticated user with import privileges write an attacker-named file into the server's process working directory instead of the isolated extraction folder. A crafted import archive whose nested entry path exceeds the 4096-byte MAX_PATH_LENGTH causes the trimFileAndExt helper to collapse the path to a bare filename, and the resulting file survives normal import cleanup. Publicly available exploit code exists per SSVC (POC), but there is no public exploit identified in the wild and EPSS probability is very low (0.04%).

Technical ContextAI

Outline is a Node.js/TypeScript collaborative documentation ('team wiki') platform that supports importing content from uploaded ZIP archives. The flaw lives in ZipHelper.extract, which builds each entry's destination by joining the sandbox directory with the entry's internal path and then passing that full filesystem path through trimFileAndExt - a filename-truncation helper that internally calls path.basename. When the joined path grows beyond MAX_PATH_LENGTH (4096 bytes), trimFileAndExt discards every directory component and returns only the base filename, so fs.createWriteStream resolves it relative to the process working directory rather than the intended extraction sandbox. This is a classic CWE-22 (Improper Limitation of a Pathname to a Restricted Directory / path traversal) root cause, here expressed not as '../' sequences but as an implicit escape triggered by a path-length edge case; cleanupExtractedData only deletes the temporary extraction directory, so the escaped artifact persists. Affected component per CPE is cpe:2.3:a:outline:outline:*:*:*:*:*:*:*:*.

RemediationAI

Vendor-released patch: upgrade Outline to 1.7.0 or later, which corrects ZipHelper.extract so extraction paths are no longer collapsed to a bare filename. If immediate upgrade is not possible, restrict who can perform document/collection imports to trusted administrators only (reducing exposure of the privileged import path), and consider temporarily disabling ZIP import workflows - the trade-off is loss of bulk-import functionality for end users. As a hardening measure, run the Outline server process from a dedicated, minimal working directory that contains no sensitive or overwritable files, so any escaped write lands in a low-value location; note this does not prevent the escape, only limits its impact. Review the advisory at https://github.com/outline/outline/security/advisories/GHSA-hw32-2v7j-mgqc for authoritative fix guidance.