CVE-2026-39977Public exploitNetwork attack vector

Host file disclosure via symlinked license paths

Published Apr 9, 2026 · Updated Apr 9, 2026

Path traversal in Flatpak flatpak-builder 1.4.5 through 1.4.7 allows attackers to read arbitrary host files through crafted build inputs. In find_defined_license_files, g_file_get_relative_path does not resolve symlinks, while the no-follow type check covers only the final component. Exploitation requires a user or CI service to process an attacker-controlled manifest or source, after which host files can be copied into distributed build output.

CVSS severity7.1
High
EPSS probability0.29%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Path traversal in Flatpak flatpak-builder 1.4.5 through 1.4.7 allows attackers to read arbitrary host files through crafted build inputs. In find_defined_license_files, g_file_get_relative_path does not resolve symlinks, while the no-follow type check covers only the final component. Exploitation requires a user or CI service to process an attacker-controlled manifest or source, after which host files can be copied into distributed build output.

The record

CVE
CVE-2026-39977
Published
Apr 9, 2026
Updated
Apr 9, 2026
Vendor
Flatpak
Product
flatpak-builder
Classifications
CWE-22, T1005
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Apr 9, 2026CVE publishedPublication date reported by the CVE source.
  2. Apr 9, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=>= 1.4.5, < 1.4.8

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Flatpak · flatpak-builderversion=>= 1.4.5, < 1.4.8

Published CVSS scores

7.1GitHub, Inc.CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N
6.3NIST NVDCVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:C/C:H/I:N/A:N

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

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No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-22Improper Limitation of a Pathname to a Restricted Directory ('Path Traversal')
T1005Data from Local System

Public exploit references

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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