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CVE-2026-55437 medium CVSS 5.4

Cross-Site Scripting (XSS) in github.com/coder/coder/v2 (CVE-2026-55437)

Summary

Cross-site scripting in github.com/coder/coder/v2 (CVE-2026-55437). Risk of unauthorized operations or information disclosure. Exploitable via AgentLogLine. Mitigation: upgrade to 2.29.17 or later.

Original description

The description as published by the source.

Summary

The AgentLogLine dashboard component instantiated ansi-to-html without escapeXML: true and inserted the result via dangerouslySetInnerHTML so HTML embedded in workspace agent log lines was rendered as live markup. Server-side sanitization did not neutralize HTML metacharacters.

Note: Exploitation requires a victim to view attacker-controlled agent logs in the dashboard.

Impact

A user who could run a workspace could emit arbitrary HTML into agent logs; when another user, including an administrator, viewed the workspace page, it rendered in their session. Content Security Policy blocked inline scripts but an attacker could still inject a meta refresh redirect, style rules for UI redressing or CSS-based exfiltration or external img beacons. This required workspace-owner access and a victim viewing the page.

Patches

The fix enables escapeXML: true so HTML metacharacters are escaped before DOM insertion.

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.

Resources

  • Fix: #25808

Credits

Coder would like to thank Anthropic's Security Team (ANT-2026-224…

Source: GitHub Security Advisories (Global) NVD GitHub Advisory

Auto-generated summary

Assembled by SecPulse from the source data (CVSS, CWE, affected versions) using templates — no AI involved. Check the original description and references below for exact details.

A vulnerability tracked as CVE-2026-55437 has been found in github.com/coder/coder/v2.
Attackers can target a specific entry point like AgentLogLine over the network to misuse the product.
Risk of unauthorized operations or information disclosure. CVSS score: 5.4/10.
What to do: upgrade github.com/coder/coder/v2 to 2.29.17 or later.
If unsure, ask your IT team or search "github.com/coder/coder/v2 CVE-2026-55437" on the vendor's site.

CVE-2026-55437 (github.com/coder/coder/v2) — CWE-79 / CVSS v3 5.4
Attack vector: remote (network-reachable)
Attack surface: AgentLogLine / dangerouslySetInnerHTML / style / img
Patched: 2.29.17 — apply immediately
Plan: 1) Audit SBOM/dependencies, 2) Stage→prod upgrade, 3) Add WAF/proxy monitoring on affected endpoints, 4) Hunt IOCs in logs.
Refs: see the GHSA / vendor advisory / patched release linked on this page.

❓ What is the problem

Cross-site scripting (XSS) (CWE-79) exists in github.com/coder/coder/v2. Attackers reach the vulnerable code path via AgentLogLine.

📍 Affected scope

Check the vendor advisory for the affected versions of github.com/coder/coder/v2. Attack surface: AgentLogLine / dangerouslySetInnerHTML / style / img.

🔥 Severity

Severity: Medium (CVSS 5.4/10). Risk of unauthorized operations or information disclosure.

🔧 How to fix

Update to 2.29.17.

🛡️ Workaround

Until the patch is applied: disable the affected feature, apply WAF rules, or restrict access via network ACLs.

🔍 Detection

Search webserver/proxy logs for unusual request patterns matching this CVE's known IOCs. Run grep -r 'github.com/coder/coder/v2' . against your dependency files (package-lock.json, requirements.txt, go.sum) to find affected services.

Response actions

Concrete steps and command examples for SOC/SRE teams to execute in order

  1. 1
    Identify exposure identify 
    grep -r 'github.com/coder/coder/v2' . | grep -v node_modules

    リポジトリと本番環境の依存ファイル (package-lock.json / requirements.txt / go.sum / Gemfile.lock 等) で github.com/coder/coder/v2 を grep し、稼働しているサービス・バージョンを把握する。

  2. 2
    Apply patch patch 
    Upgrade github.com/coder/coder/v2 to 2.29.17

    ステージング環境で 2.29.17 に上げて回帰テスト → 本番反映。回帰テストはアプリの主要ハッピーパスを含めること。

  3. 3
    Post-deployment verification verify 
    Confirm patched version is live in production

    パッチ適用後、ステージングで PoC または同等の悪用パターンを再現して脆弱性が閉じたことを確認。本番ではアクセスログ・WAF でアラート再発が無いか継続監視。

Affected packages

go github.com/coder/coder/v2
[{"type":"SEMVER","events":[{"introduced":"0"},{"fixed":"2.29.17"}]}]
Go github.com/coder/coder
[{"type":"SEMVER","events":[{"introduced":"0"}]}]

References

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