How severe is CVE-2026-55429?

CVE-2026-55429 has a CVSS score of 8.7/10, rated HIGH. Immediate patching is strongly recommended.

Which packages are affected by CVE-2026-55429?

CVE-2026-55429 affects the following packages: github.com/coder/coder/v2 (Go), github.com/coder/coder/v2 (Go), github.com/coder/coder/v2 (Go), github.com/coder/coder/v2 (Go). Ecosystems affected: Go.

How do I fix CVE-2026-55429?

Update github.com/coder/coder/v2 to 2.34.2 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-55429 is resolved across your whole dependency graph.

How do I detect CVE-2026-55429 in my Go dependencies?

Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for github.com/coder/coder/v2, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

How do I mitigate CVE-2026-55429 if there is no patch (or I can't update yet)?

If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.

Is CVE-2026-55429 actively exploited in the wild?

No public exploit code has been indexed for CVE-2026-55429 yet. This does not mean the vulnerability cannot be exploited — absence of public exploits does not imply safety. Apply the recommended fix and use O3 Security to monitor your exposure.

What is the EPSS score for CVE-2026-55429?

CVE-2026-55429 has an EPSS (Exploit Prediction Scoring System) score of 0.5%, placing it in the 42th percentile of all CVEs. EPSS is maintained by FIRST.org and estimates the probability that a vulnerability will be exploited in the wild within the next 30 days. This score indicates relatively lower exploitation probability, though the CVSS severity should still guide your patching priority.

What type of vulnerability is CVE-2026-55429?

CVE-2026-55429 is classified as CWE-639 (CWE-639). This weakness type describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation.

When was CVE-2026-55429 published, and has it been updated?

CVE-2026-55429 was published on July 8, 2026 and was last updated on October 21, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

🐹

🐹 Go

Not in CISA KEV

HIGH severity

CVE-2026-55429 — coder

HIGHFix: coder/coder#26103

CVE-2026-55429 is a high-severity (CVSS 8.7) CWE-639 vulnerability in github.com/coder/coder/v2. A fix is available for github.com/coder/coder/v2 — see the affected versions and patch details below.

Coder's workspace app upsert allows cross-workspace agent rebinding via user-controlled app ID

Also known asGHSA-9rjw-3gwp-f59vGO-2026-5909

Published

Jul 8, 2026

Updated

Oct 21, 2026

Affected

4 pkgs

Patched

4 / 4

Exploits

None indexed

Exploitation data as of Oct 22, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

Exploitation Status

No confirmed exploitation observed yet

CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.

Exploitation and automatability from CISA’s SSVC triage for CVE-2026-55429.

EPSS Exploitation Probability

via FIRST.org ↗

0.5%probability of exploitation in next 30 days

Lower Risk0.00%

Lower risk than most CVEs42th percentile — riskier than 42% of all scored CVEsHighest risk

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

How urgent is this, really

CVE-2026-55429 by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.

Where this sits among everything scored

Of 395,249 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Counts from FIRST.org, log-scaled.

Real-World Exposure

4 pkgs affected

🐹github.com/coder/coder/v2🐹github.com/coder/coder/v2🐹github.com/coder/coder/v2🐹github.com/coder/coder/v2

Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects Go packages — download data is not available via public APIs for these ecosystems.

Description

Summary

UpsertWorkspaceApp overwrites an existing app's agent_id on a primary-key conflict and insertAgentApp accepts the app ID from the provisioner's CompleteJob payload without verifying it belongs to the workspace being built. CompleteJob runs under dbauthz.AsProvisionerd so the authorization layer does not block the cross-workspace upsert.

Note: Exploitation requires elevated access as a template author or external provisioner operator.

Impact

A user with template authorship or external provisioner access can submit a CompleteJob payload with a known victim app UUID and an attacker-controlled agent ID. On completion of the attacker's build the victim's app row is rebound to the attacker's agent so later app traffic such as IDE and terminal sessions is proxied to the attacker's workspace. App UUIDs are discoverable through the public API.

Patches

The fix verifies that any existing workspace_apps row matching the supplied ID belongs to the workspace being built and rejects cross-workspace agent reassignment.

The fix was backported to all supported release lines:

Release line	Patched version
2.34	v2.34.2
2.33	v2.33.8
2.32	v2.32.7
2.29 (ESR)	v2.29.17

Workarounds

None. Upgrading is required.

Resources

Fix: #26103

Credits

Coder would like to thank Anthropic's Security Team (ANT-2026-22441) for independently disclosing this issue!

Affected Packages

4 total 4 fixed

Ecosystem	Package	Vulnerable range	Fix
🐹Go	`github.com/coder/coder/v2`	≥ 2.34.0&&< 2.34.2	2.34.2`go get github.com/coder/coder/v2@v2.34.2`
🐹Go	`github.com/coder/coder/v2`	≥ 2.33.0&&< 2.33.8	2.33.8`go get github.com/coder/coder/v2@v2.33.8`
🐹Go	`github.com/coder/coder/v2`	≥ 2.30.0&&< 2.32.7	2.32.7`go get github.com/coder/coder/v2@v2.32.7`
🐹Go	`github.com/coder/coder/v2`	all versions	2.29.17`go get github.com/coder/coder/v2@v2.29.17`

Affected Products

1 product · 4 configurations

Application

codercoder

≥ 2.34.0 && < 2.34.2

range

Detection & mitigation playbook

Open-source dependency

Detect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for github.com/coder/coder/v2, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update github.com/coder/coder/v2 to 2.34.2 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-55429 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.

Frequently Asked Questions

### Summary `UpsertWorkspaceApp` overwrites an existing app's `agent_id` on a primary-key conflict and `insertAgentApp` accepts the app ID from the provisioner's `CompleteJob` payload without verifying it belongs to the workspace being built. `CompleteJob` runs under `dbauthz.AsProvisionerd` so the authorization layer does not block the cross-workspace upsert. > **Note:** Exploitation requires elevated access as a template author or external provisioner operator. ### Impact A user with template authorship or external provisioner access can submit a `CompleteJob` payload with a known victim