Cyber Resilience

CVE-2026-31893

Tunnelblick 3.5.3 – 8.0.1

Public PoC
Published
05 May 2026
Modified
25 July 2026
Patch / advisory
View advisory
CVSS Score v4 6.8
Click a component to see what it means
Raw vectorCVSS:4.0/AV:L/AC:L/AT:N/PR:L/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
EPSS Score 0.0024 15th percentile
Risk Priority 29 floored blend · peak EPSS

CVSS and EPSS are reproduced from their sources (NVD, FIRST EPSS). Risk Priority is our own derived reading, not an NVD score.

Summary

CVE-2026-31893 is a medium-severity UNIX Symbolic Link (Symlink) Following (CWE-61) vulnerability in Tunnelblick Tunnelblick. Its CVSS base score is 6.8 (Medium).

Operationally, exploitation aligns with the MITRE ATT&CK technique Path Interception (T1034); ranked at the 15th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog; a public proof-of-concept is referenced.

The strongest mitigations our analysis identified map to AC-3 (Access Enforcement) and AC-4 (Information Flow Enforcement) — see the control section below for these in your framework.

OWASP Top 10 for Web (2025)

A01:2025 Broken Access Control

EU & UK References

Vulnerability Data

Tunnelblick is an open source graphic user interface for OpenVPN on macOS. In versions 3.3beta26 through 9.0beta01, any local user can read arbitrary root-owned files by exploiting a symlink following vulnerability in tunnelblick-helper, reachable through the world-accessible tunnelblickd Unix socket.…

more

The socket is configured with mode 0666, allowing any local user to connect. No authorization check is performed on the connecting client. The tunnelblick-helper process constructs a path to config.ovpn inside a user-controlled .tblk directory and reads it as root without symlink validation. An attacker can create a .tblk configuration with a symlinked config.ovpn pointing to any file and request tunnelblickd to read it. This issue has been fixed in versions 9.0beta02.

CWE(s)
CWE-61

Related Threats

MITRE ATT&CK Enterprise Techniques

T1034 Path Interception Persistence
**This technique has been deprecated.
attack.mitre.org →
Derived from this CVE’s CWE(s) via the direct CWE→ATT&CK cross-walk.

CVEs Like This One

CVE-2026-12958Shared CWE-61
CVE-2025-5468Shared CWE-61
CVE-2024-42367Shared CWE-61
CVE-2026-29203Shared CWE-61
CVE-2025-3047Shared CWE-61
CVE-2026-54574Shared CWE-61
CVE-2026-33056Shared CWE-61
CVE-2025-54867Shared CWE-61
CVE-2026-22767Shared CWE-61
CVE-2026-1386Shared CWE-61

Affected Assets

tunnelblick
tunnelblick
3.3, 8.1, 9.0 · 3.5.3 — 8.0.1

Mitigating Controls

Control response

Prevent
Stop it (NIST 800-53)

—

Detect
Catch it (NIST detect / respond)

—

Harden
Shrink the surface (DISA STIG)
  • 2 hardening rules · 2 OS baselines
Validate
Prove the fix (OWASP ASVS)
  • V5.2.5

Mitigating Controls (NIST 800-53 r5) AI

AC-3 Access Enforcement good match

Access enforcement must resolve the actual target of any file reference and apply authorizations to it, directly stopping symlink traversal to unauthorized objects.

AC-4 Information Flow Enforcement partial match

Information-flow enforcement on file operations must follow the resolved target rather than the link name, blocking unauthorized data movement via symlinks.

AC-6 Least Privilege partial match

Least-privilege restrictions on the directories that may contain links or targets reduce the set of files an attacker can reach even if a symlink is followed.

Mitigating Controls (NIST CSF 2.0) AI

Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→CSF cross-walk (authority under review) — links open the control.

PR.PS-06 mostly match
prevents

Secure SDLC practices directly prevent introduction of symlink-following flaws in file-handling code.

ID.RA-01 partial match
prevents

Vulnerability identification can discover existing symlink issues but does not prevent or remediate them in code.

PR.AA-05 partial match
prevents

Least-privilege access policies can limit damage from symlink attacks but do not address the coding flaw itself.

Mitigating Controls (ISO/IEC 27001:2022 Annex A) AI

Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→ISO cross-walk (authority under review) — links open the control.

A.8.29 Security testing in development and acceptance mostly match
finds

Security testing can detect symlink-following vulnerabilities before deployment, covering most of the weakness.

A.8.27 Secure system architecture and engineering principles partial match
prevents

Secure-architecture principles require safe file-handling and canonicalization, directly addressing symlink attacks.

A.8.28 Secure coding partial match
prevents

Secure-coding standards mandate explicit symlink checks and safe open patterns, fully mitigating CWE-61.

A.8.3 Information access restriction partial match
mitigates

Access-control rules can restrict which files a process may open, reducing symlink-following risk but not eliminating the underlying path-resolution flaw.

Hardening callouts derived

Configuration rules from DISA STIG baselines that bear on weaknesses of the type cited by this CVE. Each rule is shown with the relationship its mapping actually records, against the CWE it was authored against. Derived via CVE→CWE over `controls_xwalks` (authoritative rows only; rows rated `none` are excluded).

Oracle Linux 8 (1 rule)
  • V-248577 OL 8 must enable kernel parameters to enforce Discretionary Access Control (DAC) on symlinks. prevents CWE-61

References