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CVE-2026-53551

Vulnerability in github.com/free5gc/free5gc (CVE-2026-53551)

Summary

Vulnerability in github.com/free5gc/free5gc (CVE-2026-53551). Risk of unauthorized operations or information disclosure. Exploitable via POST /nausf-auth/v1/ue-authentications. Mitigation: upgrade to 4.2.2 or later.

Original description

The description as published by the source.

Summary

The free5GC AUSF (Authentication Server Function) does not validate the supiOrSuci field in UE authentication requests. Null bytes (\x00) and other control characters pass through JSON parsing unchanged and are forwarded to the UDM in an unescaped URL path. This causes Go's net/url.Parse() to fail, returning HTTP 500 "System failure" and leaking internal stack traces. An unauthenticated attacker can trigger this at scale—4.1% of special_chars mutations produce HTTP 500—causing denial of service for all subscribers attempting authentication through the affected AUSF. CWE-20 (Improper Input Validation).

Details

The vulnerability lies in the AUSF's POST /nausf-auth/v1/ue-authentications handler. The JSON body includes a supiOrSuci field:

{"supiOrSuci": "imsi-208930000000031", "servingNetworkName": "...", "authType": "5G_AKA"}

The AUSF parses this JSON (Go's encoding/json accepts null bytes in strings per RFC 8259), then constructs a UDM URL by directly embedding the raw supiOrSuci value:

GET /nudm-ueau/v1/{supiOrSuci}/security-information/...

When supiOrSuci contains null bytes (\x00), the resulting URL is illegal under RFC 3986. Go's net/url.Parse() fails, and the error propagates as an unhandled internal error, returning HTTP 500 with a stack trace in the response body:

{"error":{"status":"INTERNAL_SERVER_ERROR","message":"System failure"}}

The AUSF container log shows: `net/url: invalid control ch…

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-2026-53551 has been found in github.com/free5gc/free5gc.
Attackers can target a specific entry point like POST /nausf-auth/v1/ue-authentications over the network to misuse the product.
Risk of unauthorized operations or information disclosure.
What to do: upgrade github.com/free5gc/free5gc to 4.2.2 or later.
If unsure, ask your IT team or search "github.com/free5gc/free5gc CVE-2026-53551" on the vendor's site.

CVE-2026-53551 (github.com/free5gc/free5gc) — CWE-20
Attack surface: POST /nausf-auth/v1/ue-authentications / GET /nudm-ueau/v1/{supiOrSuci}/security-information/... / GET /nudm-ueau/v1/imsi- / supiOrSuci
Patched: 4.2.2 — 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

A vulnerability (CWE-20) exists in github.com/free5gc/free5gc. Attackers reach the vulnerable code path via POST /nausf-auth/v1/ue-authentications.

📍 Affected scope

Check the vendor advisory for the affected versions of github.com/free5gc/free5gc. Attack surface: POST /nausf-auth/v1/ue-authentications / GET /nudm-ueau/v1/{supiOrSuci}/security-information/... / GET /nudm-ueau/v1/imsi- / supiOrSuci.

🔥 Severity

Severity: ?. Risk of unauthorized operations or information disclosure.

🔧 How to fix

Update to 4.2.2.

🛡️ 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 POST /nausf-auth/v1/ue-authentications requests with malformed payloads or SQL meta-characters. Run grep -r 'github.com/free5gc/free5gc' . 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/free5gc/free5gc' . | 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/free5gc/free5gc 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
    Hunt for indicators of compromise detect 
    grep 'POST /nausf-auth/v1/ue-authentications' /var/log/nginx/access.log | grep -E '(unusual_payload|sqli_pattern)'

    アクセスログで POST /nausf-auth/v1/ue-authentications への異常なリクエスト (不正な認証ヘッダ・SQLメタ文字)を過去 30〜90日分捜索。WAF/SIEM があれば該当パスのアラート発火履歴を確認。

  3. 3
    Apply patch patch 
    Upgrade github.com/free5gc/free5gc to 4.2.2

    ステージング環境で 4.2.2 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と、Step 2 で見つけた異常検知の続報チェックを含めること。

  4. 4
    Post-deployment verification verify 
    Replay attack against POST /nausf-auth/v1/ue-authentications on staging to confirm patch closes the vector

    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 Step 2 と同じログクエリでアラート再発が無いか継続監視。

Affected packages

go github.com/free5gc/free5gc
[{"type":"SEMVER","events":[{"introduced":"0"},{"fixed":"4.2.2"}]}]
go github.com/free5gc/ausf
[{"type":"SEMVER","events":[{"introduced":"0"},{"fixed":"1.4.5"}]}]

References

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