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CVE-2026-55079 medium CVSS 4.9

Vulnerability in github.com/coder/coder/v2 (CVE-2026-55079)

Summary

Vulnerability in github.com/coder/coder/v2 (CVE-2026-55079). Risk of unauthorized operations or information disclosure. Exploitable via NewDataBuilder. Mitigation: upgrade to 2.29.17 or later.

Original description

The description as published by the source.

Summary

NewDataBuilder in provisionersdk/proto/dataupload.go allocated a byte slice using the client-supplied FileSize from a DataUpload message without an upper-bound check. Although the DRPC wire limit is 4 MiB, the FileSize value itself was unconstrained

Impact

An authenticated user able to reach the provisioner daemon serve endpoint could send a roughly 50-byte message declaring a huge FileSize (for example 1 TiB), triggering an unrecoverable Go out-of-memory abort that terminates coderd. This is a single-message denial of service affecting the entire deployment.

Patches

The fix validates FileSize against an upper bound (MaxFileSize = 100 MiB) before allocation.

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

Restrict access to the provisioner daemon serve endpoint to trusted provisioner daemon service accounts.

Resources

  • Fix: #25710

Credits

Coder would like to thank Anthropic's Security Team (ANT-2026-22442) for independently disclosing this issue!

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-2026-55079 has been found in github.com/coder/coder/v2.
Attackers can target a specific entry point like NewDataBuilder over the network to misuse the product.
Risk of unauthorized operations or information disclosure. CVSS score: 4.9/10.
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-2026-55079" on the vendor's site.

CVE-2026-55079 (github.com/coder/coder/v2) — CWE-789 / CVSS v3 4.9
Attack vector: remote (network-reachable) / no user interaction
Attack surface: NewDataBuilder / FileSize / DataUpload / coderd
Patched: 2.29.17 — apply immediately
Workaround: Restrict access to the provisioner daemon serve endpoint to trusted provisioner daemon service accounts.
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

A vulnerability (CWE-789) exists in github.com/coder/coder/v2. Attackers reach the vulnerable code path via NewDataBuilder.

📍 Affected scope

Check the vendor advisory for the affected versions of github.com/coder/coder/v2. Attack surface: NewDataBuilder / FileSize / DataUpload / coderd.

🔥 Severity

Severity: Medium (CVSS 4.9/10). Risk of unauthorized operations or information disclosure.

🔧 How to fix

Update to 2.29.17.

🛡️ Workaround

Workaround: Restrict access to the provisioner daemon serve endpoint to trusted provisioner daemon service accounts.

🔍 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 temporary workaround mitigate 
    Restrict access to the provisioner daemon serve endpoint to trusted provisioner daemon service accounts.

    パッチが適用されるまでの応急処置として、Restrict access to the provisioner daemon serve endpoint to trusted provisioner daemon service accounts. を実施。回避策の副作用 (機能低下) を確認した上で。

  3. 3
    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。

  4. 4
    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":"2.24.0"},{"fixed":"2.29.17"}]}]
Go github.com/coder/coder
[{"type":"SEMVER","events":[{"introduced":"0"}]}]

References

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