CVE-2026-39977
Description
A flaw was found in flatpak-builder. A specially crafted manifest or source can bypass path restrictions by using symbolic links within the license-files field, allowing the builder to follow paths outside the intended source directory, reading arbitrary files from the host system and including them in the build output. As a result, sensitive data from the host environment may be exposed in the resulting application package.
Statement
To exploit this issue, an attacker needs to convince a user to build a package via a crafted manifest or source, specifically, with a malicious license-files field. In automated build systems where untrusted packages may be processed, this issue can be exploited without user interaction but the attacker still has to introduce a malicious manifest into the build queue. Due to these reasons, this flaw has been rated with a moderate severity.
Mitigation
To mitigate this issue, audit untrusted manifests and sources for suspicious license-files paths. Additionally, consider running the build process inside a container or a restricted sandbox environment to ensure the builder cannot access sensitive host files or credentials.
Common Vulnerability Scoring System (CVSS) Score Details
Info alert:Important note
CVSS scores for open source components depend on vendor-specific factors (e.g. version or build chain). Therefore, Red Hat's score and impact rating can be different from NVD and other vendors. Red Hat remains the authoritative CVE Naming Authority (CNA) source for its products and services (see Red Hat classifications).
The following CVSS metrics and score provided are preliminary and subject to review.
CVSS v3 Score Breakdown
| Red Hat | NVD | cve.org | |
|---|---|---|---|
| Base Score | 6.3 | 6.3 | N/A |
| Attack Vector | Local | Local | N/A |
| Attack Complexity | Low | Low | N/A |
| Privileges Required | None | None | N/A |
| User Interaction | Required | Required | N/A |
| Scope | Changed | Changed | N/A |
| Confidentiality | High | High | N/A |
| Integrity Impact | None | None | N/A |
| Availability Impact | None | None | N/A |
Vector
Red Hat: CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:C/C:H/I:N/A:N
NVD: CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:C/C:H/I:N/A:N
Understanding the Weakness (CWE)
Integrity,Confidentiality,Availability
Technical Impact: Execute Unauthorized Code or Commands
The attacker may be able to create or overwrite critical files that are used to execute code, such as programs or libraries.
Integrity
Technical Impact: Modify Files or Directories
The attacker may be able to overwrite or create critical files, such as programs, libraries, or important data. If the targeted file is used for a security mechanism, then the attacker may be able to bypass that mechanism. For example, appending a new account at the end of a password file may allow an attacker to bypass authentication.
Confidentiality
Technical Impact: Read Files or Directories
The attacker may be able read the contents of unexpected files and expose sensitive data. If the targeted file is used for a security mechanism, then the attacker may be able to bypass that mechanism. For example, by reading a password file, the attacker could conduct brute force password guessing attacks in order to break into an account on the system.
Availability
Technical Impact: DoS: Crash, Exit, or Restart
The attacker may be able to overwrite, delete, or corrupt unexpected critical files such as programs, libraries, or important data. This may prevent the product from working at all and in the case of protection mechanisms such as authentication, it has the potential to lock out product users.
Frequently Asked Questions
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