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Flatpak EUVDEUVD-2026-19970

| CVE-2026-34078 CRITICAL
UNIX Symbolic Link (Symlink) Following (CWE-61)
2026-04-07 GitHub_M
RCE Flatpak
Critical
Disputed · 9.3 Vendor: GitHub_M
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Attack ChainAIDerived

Hypothetical attack flow derived from CVE metadata – not a confirmed exploit chain

  1. Access
    Create symlink in sandbox
  2. Delivery
    Point symlink to arbitrary host path
  3. Exploit
    Invoke sandbox-expose option
  4. Execution
    Access host files in sandbox
  5. Impact
    Execute code in host context

Vulnerability Assessment

Weakness
CWE
CWE-61
OWASP Top 10:2025
A01:2025 - Broken Access Control
ASVS 5.0
V5 - File Handling UNIX symlink resolution
Exploitation Conditions

Flatpak versions prior to 1.16.4 running on Linux. Attacker must be able to create symlinks within a sandboxed Flatpak application. The application uses sandbox-expose options with attacker-controlled paths. No user interaction required; exploitation occurs when Flatpak mounts the symlink-resolved host path.
Impact

This vulnerability represents a critical security boundary violation with real-world exploitation potential, though risk signals are mixed. The CVSS v4.0 score of 9.3 reflects maximum severity across confidentiality, integrity, and availability impacts (VC:H/VI:H/VA:H) with network attack vector (AV:N), low complexity (AC:L), and no privileges required (PR:N). However, the network vector designation appears inconsistent with typical Flatpak deployment models where exploitation would require an already-installed malicious application, suggesting local attack context. No EPSS score was provided, and CISA KEV status is negative, indicating no confirmed active exploitation in the wild. The SSVC decision framework suggests high priority: the vulnerability is technically exploitable (symlink primitives are well-understood), likely automatable once an app is installed, and has complete host compromise as technical impact. The primary mitigating factor is that exploitation requires convincing a user to install a malicious Flatpak application first, which reduces immediate internet-scale risk but remains serious for supply chain or trojanized app scenarios. The availability of a vendor patch (1.16.4) and clear technical documentation in the GitHub Security Advisory elevates this to a mandatory remediation for any Linux environment using Flatpak for application isolation.
Exploit ScenarioDerived

An attacker distributes a seemingly legitimate Flatpak application through third-party repositories or social engineering (e.g., a gaming utility, media converter, or productivity tool). Once a user installs and runs the malicious application, it creates symbolic links within its sandbox pointing to sensitive host directories such as /etc/shadow, /root/.ssh, or system binary directories. The app then invokes Flatpak portal APIs with sandbox-expose options referencing these symlinks. Flatpak resolves the symlinks and mounts the actual host paths into the sandbox, giving the malicious app read/write access to host authentication databases, SSH keys, or the ability to replace system binaries. The attacker can exfiltrate credentials, install persistent backdoors in host startup scripts, or achieve full root-level code execution by replacing privileged binaries with trojaned versions. This scenario requires low attack complexity (AC:L) as symlink creation is trivial within the sandbox, and no user interaction beyond initial app installation (UI:N in ongoing exploitation).
Act Now Prioritize within 24-48h. Why: CRITICAL severity.
Patch available 0.2% exploitation probability (EPSS)

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AnalysisAIv1 – Apr 07, 2026

Sandbox escape in Flatpak versions prior to 1.16.4 allows applications to access arbitrary host filesystem paths and achieve host-level code execution through symlink manipulation in portal sandbox-expose options. The vulnerability requires no authentication (CVSS:4.0 PR:N) and is exploitable over the network with low complexity. No confirmed active exploitation (CISA KEV) or public exploit code identified at time of analysis, though the attack primitive is clearly documented in the vendor advisory.

RemediationAI

Immediately upgrade Flatpak to version 1.16.4 or later, which contains the complete fix for symlink resolution vulnerabilities in portal sandbox-expose handling. Linux distribution users should apply patches through their package manager (e.g., 'dnf update flatpak', 'apt update && apt upgrade flatpak') as downstream vendors backport the security fix. System administrators should verify the installed version with 'flatpak --version' and confirm it shows 1.16.4 or higher post-update. No effective workarounds exist that maintain Flatpak functionality while mitigating the vulnerability, as the issue is fundamental to portal path handling logic. Organizations unable to immediately patch should consider temporarily restricting Flatpak application installations to trusted sources only and auditing existing installed applications for suspicious behavior. Consult the official vendor security advisory at https://github.com/flatpak/flatpak/security/advisories/GHSA-cc2q-qc34-jprg for additional context and detection guidance. After patching, review installed Flatpak applications and remove any from untrusted or unknown sources.

Affected VersionsENISA

flatpak < 1.16.4

Affected Packages

euvd flatpak fix: 1.16.4

Source: OSV (Open Source Vulnerabilities)

Affects your stack

Affects 1 package in euvd

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Technical ContextAI · show details

Flatpak is a Linux application sandboxing framework designed to isolate containerized applications from the host system. The vulnerability (CWE-61: UNIX Symbolic Link Following) exists in the Flatpak portal's handling of sandbox-expose options. The portal service, which mediates controlled access between sandboxed apps and host resources, fails to properly validate or sanitize paths containing symbolic links. When an application provides a symlink path through sandbox-expose options, Flatpak resolves the symlink and mounts the target host path directly into the sandbox filesystem namespace. Because applications can control the creation and destination of symlinks within their sandbox environment, they can craft symlinks pointing to sensitive host directories (such as /etc, /root, or system binaries). The portal then grants the sandboxed app direct access to these resolved paths, completely bypassing the intended security boundary. This affects all deployments using Flatpak versions earlier than 1.16.4 where applications can influence sandbox-expose parameters.

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Severity by source

Sources disagree (Medium–Critical)
Vendor (GitHub_M) PRIMARY 9.3 CRITICAL
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N
SUSE 8.2 HIGH
AV:L/AC:L/PR:L/UI:R/S:C/C:H/I:H/A:H
Red Hat 8.2 MEDIUM

vuln.today treats the vendor’s rating as authoritative. A higher third-party CVSS (e.g. CISA-ADP) is shown for transparency but does not drive the headline severity.

CVSS VectorVendor: GitHub_M

Attack Vector
Network
Attack Complexity
Low
Attack Requirements
None
Privileges Required
None
User Interaction
None
Vulnerable system: Confidentiality
High
Vulnerable system: Integrity
High
Vulnerable system: Availability
High
Subsequent system: Confidentiality
None
Subsequent system: Integrity
None
Subsequent system: Availability
None

Lifecycle Timeline

3
Analysis Updated
Apr 16, 2026 - 05:45 EUVD-patch-fix
executive summary
Patch available
Apr 16, 2026 - 05:29 EUVD
1.16.4
CVE Published
Apr 07, 2026 - 21:27 nvd
CRITICAL 9.3

DescriptionCVE.org

Flatpak is a Linux application sandboxing and distribution framework. Prior to 1.16.4, the Flatpak portal accepts paths in the sandbox-expose options which can be app-controlled symlinks pointing at arbitrary paths. Flatpak run mounts the resolved host path in the sandbox. This gives apps access to all host files and can be used as a primitive to gain code execution in the host context. This vulnerability is fixed in 1.16.4.

Executive ViewAI

Why It Matters

Flatpak versions before 1.16.4 contain a critical sandbox escape vulnerability that allows containerized applications to bypass security controls and execute code at the host system level through symlink manipulation. This directly threatens organizations running Flatpak-containerized applications, as compromised or malicious apps can gain unrestricted access to sensitive data and system resources across the entire infrastructure.

Business Impact: Severe
Compensating Controls

Apply vendor patch. Until upgrade is complete: restrict Flatpak application execution to trusted applications only; disable network access for Flatpak containers where operationally feasible; enforce host-level filesystem access controls to limit exposure even if sandbox is breached.

Threat Intelligence Overview

EPSS Score
0.2%
Top 64% exploitable
Data Quality
8 sources
Confidence: High
EUVD NVD CVE.org EPSS Vulnrichment Vendor GitHub VulDB

How this decision was reached

The engine reads each signal below and applies a fixed list of rules from top to bottom. The first rule that matches sets the recommended action – like a statement, every line is shown.

SignalValue
Severity CRITICAL
CISA KEV No
Public POC No
EPSS 0.2%
Patch available Yes
Active threat No
Deciding rule
CRITICAL severity
What every action level means
Emergency Immediate action required. Criteria: CRITICAL + in CISA KEV (actively exploited) without patch, OR CRITICAL + EPSS > 30% without patch, OR CRITICAL + active threat signals without patch.
Act Now Prioritize within 24-48h. Criteria: in KEV with patch available, OR CRITICAL + public POC, OR HIGH + EPSS > 10%, OR CRITICAL + active threat, OR any CRITICAL severity.
This Week Schedule remediation this week. Criteria: HIGH severity (CVSS 7.0-8.9). Patch within normal change window.
This Month Plan within 30 days. Criteria: MEDIUM severity (CVSS 4.0-6.9), lower exploitation probability. Include in regular patch cycle.
Monitor Track and reassess. Criteria: LOW severity (CVSS 0.1-3.9), minimal exploitation risk. No immediate action needed.

SSVC AssessmentENISA

SSVC Decision
Out-of-Cycle
Exploitation
None
System Exposure· derived
Open
Automatable
Yes
Human Impact
Very High
Technical Impact
Total

Priority Score

46
Low Medium High Critical
KEV: 0
EPSS: 0
CVSS: +46
PoC: 0
Weaponized: 0
Threat intel: 0
Gov advisory: 0

Attack Technique

Remote Code Execution CRITICAL

Remote Code Execution represents the critical moment when an attacker successfully runs arbitrary code on a target system without physical access.

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Same weakness CWE-61 – UNIX Symbolic Link (Symlink) Following

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Vendor StatusVendor

SUSE

Severity: High
Product Status
openSUSE Tumbleweed Fixed
SUSE Linux Enterprise High Performance Computing 15 SP4-ESPOS Affected
SUSE Linux Enterprise High Performance Computing 15 SP4-LTSS Affected
SUSE Linux Enterprise High Performance Computing 15 SP5-ESPOS Affected
SUSE Linux Enterprise High Performance Computing 15 SP5-LTSS Affected

References

Advisories & patches
ADVISORY https://ubuntu.com/security/notices/USN-8741-1 ADVISORY https://vuldb.com/vuln/355976 REF http://www.openwall.com/lists/oss-security/2026/04/09/8 REF http://www.openwall.com/lists/oss-security/2026/04/10/14 REF https://access.redhat.com/errata/RHSA-2026:21755 REF https://access.redhat.com/errata/RHSA-2026:21756 REF https://access.redhat.com/errata/RHSA-2026:21757 REF https://access.redhat.com/errata/RHSA-2026:23417 REF https://access.redhat.com/errata/RHSA-2026:23418 REF https://access.redhat.com/errata/RHSA-2026:23419 REF https://access.redhat.com/errata/RHSA-2026:23420 REF https://access.redhat.com/errata/RHSA-2026:25068 REF https://access.redhat.com/errata/RHSA-2026:25381 REF https://access.redhat.com/errata/RHSA-2026:30901 REF https://access.redhat.com/errata/RHSA-2026:35843 REF https://access.redhat.com/security/cve/CVE-2026-34078 REF https://bugzilla.redhat.com/show_bug.cgi?id=2456276 REF https://github.com/flatpak/flatpak/security/advisories/GHSA-cc2q-qc34-jprg REF https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-34078.json

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