CVE-2026-12609: In Eclipse Theia versions 1.66.0 and up until including 1.73.1, the `@theia/plugin-ext` backend exposes the `/

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HIGH 7.5REMOTEUPGRADE

CVE-2026-12609 is a high-severity flaw (CVSS 7.5) affecting theia. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

In Eclipse Theia versions 1.66.0 and up until including 1.73.1, the `@theia/plugin-ext` backend exposes the `/hostedPlugin/:pluginId/:path(*)` HTTP endpoint, which resolves the requested file path with `path.resolve(localPath, filePath)` without verifying that the resolved path stays within the plugin's directory. An unauthenticated network attacker can send percent-encoded `../` sequences (`%2e%2e%2f`) that decode into the path parameter and esc

Why this priority

High severity
Remotely exploitable, no login, no user action

A fixed release or distro patch exists.

Risk facts

CVSS score	7.5 (High)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	1.6% (top 24%)
CISA exploited list	No
Weakness	CWE-22
Published	2026-08-05
Last modified	2026-10-23

Publisher (CNA): Eclipse Foundation · Vendor: eclipse

Am I affected?

Timeline

2026-08-05 11:16 UTCPublished CVE record published
2026-10-23 21:10 UTCUpdated Record last modified

eclipse theia UPGRADE

Affected: >= 1.66.0 and < 1.74.0

Fixed in: 1.74.0

Safe to downgrade to: a release before 1.66.0

1. Check installed version

apt-cache policy theia || rpm -q theia || theia --version

2. UPGRADE to 1.74.0 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade theia

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade theia

Note

Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.

3. If no update is available yet, DOWNGRADE to a release before 1.66.0 (Debian / Ubuntu)

apt-cache madison theia sudo apt install theia=<VERSION_BEFORE_1.66.0> sudo apt-mark hold theia

3. If no update is available yet, DOWNGRADE (RHEL / Amazon Linux / Fedora)

dnf --showduplicates list theia sudo dnf downgrade theia-<VERSION_BEFORE_1.66.0> sudo dnf versionlock add theia

Downgrade risk

Downgrading can break dependent software and may reopen older bugs. Read the distro advisory first and test on a non-production host.

After downgrade

Restart the service, and keep the package held until a fixed release ships.

Exact fixes by distribution

Fedora 46 · python-streamlink · FIXED · 8.6.2-1.fc46 · FEDORA-2026-a56fcfdc08 · source

sudo dnf upgrade --advisory=FEDORA-2026-a56fcfdc08

Fedora ELN · valgrind · FIXED · 3.28.0-1.eln159 · FEDORA-2026-c593ef1d15 · source

sudo dnf upgrade --advisory=FEDORA-2026-c593ef1d15

Public exploits and detection

Public code exists for this CVE. Treat unpatched systems as at risk, and only run PoCs in a lab.

Nuclei scan template: Eclipse Theia - Unauthenticated Path Traversal

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Related CVEs

CVE-2026-60009 HIGH 8.8 UPGRADE In Eclipse Theia versions up to and including 1.73.1, the `@theia/filesystem` backend binds `POST /file-upload
CVE-2026-61891 HIGH 7.5 UPGRADE In Eclipse Theia versions up to and including 1.73.1, the `@theia/filesystem` backend exposes HTTP file-downlo
CVE-2026-14574 MEDIUM 6.5 UPGRADE In Eclipse Theia versions 0.7.0 and up until including 1.73.1, the `PreferenceUtils.merge` function in `@theia

References

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