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CVE-2026-55785 low CVSS 3.7

Vulnerability in github.com/free5gc/ausf (CVE-2026-55785)

Summary

Vulnerability in github.com/free5gc/ausf (CVE-2026-55785). Risk of unauthorized operations or information disclosure. Exploitable via AT_MAC. Mitigation: upgrade to 1.4.5 or later.

Original description

The description as published by the source.

Summary

The AUSF component of free5GC compares authentication response values with normal Go equality helpers instead of constant-time cryptographic comparison functions.

Two authentication flows are affected in internal/sbi/processor/ue_authentication.go:

  1. 5G-AKA confirmation compares RES* and XRES* with strings.EqualFold().
  2. EAP-AKA' confirmation compares AT_MAC with bytes.Equal() and compares XRES and RES with ==.

These functions are not designed to be constant-time cryptographic comparators and may return earlier depending on the location of the first mismatch.

Additionally, the 5G-AKA confirmation path logs both the received res* and the expected Xres* at INFO level immediately before comparing them. The XRES* value is authentication material and should not be written to application logs.

The timing side channel was confirmed as a code issue, but practical exploitation over HTTP was not demonstrated in the lab because the comparator-level signal is much smaller than HTTP/SBI noise. The XRES* logging issue is directly observable in AUSF logs.

Confirmed on github.com/free5gc/ausf v1.4.4 and current main as of the May 2026 analysis.

Details

5G-AKA: RES* / XRES*

In Auth5gAkaComfirmRequestProcedure(), the AUSF logs both values and then compares them with strings.EqualFold():

// internal/sbi/processor/ue_authentication.go
logger.Auth5gAkaLog.Infof("res*: %x\nXres*: %x\n",
    updateConfirmationData.ResStar,…

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-2026-55785 has been found in github.com/free5gc/ausf.
Attackers can target a specific entry point like AT_MAC over the network to misuse the product.
Risk of unauthorized operations or information disclosure. CVSS score: 3.7/10.
What to do: upgrade github.com/free5gc/ausf to 1.4.5 or later.
If unsure, ask your IT team or search "github.com/free5gc/ausf CVE-2026-55785" on the vendor's site.

CVE-2026-55785 (github.com/free5gc/ausf) — CWE-208 / CVSS v3 3.7
Attack vector: remote (network-reachable) / unauthenticated / no user interaction
Attack surface: AT_MAC / XRES / RES / XresStar
Patched: 1.4.5 — 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-208) exists in github.com/free5gc/ausf. Attackers reach the vulnerable code path via AT_MAC without authentication.

📍 Affected scope

Check the vendor advisory for the affected versions of github.com/free5gc/ausf. Attack surface: AT_MAC / XRES / RES / XresStar.

🔥 Severity

Severity: Low (CVSS 3.7/10). Risk of unauthorized operations or information disclosure.

🔧 How to fix

Update to 1.4.5.

🛡️ 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/free5gc/ausf' . 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/ausf' . | 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/ausf 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/free5gc/ausf to 1.4.5

    ステージング環境で 1.4.5 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/free5gc/ausf
[{"type":"SEMVER","events":[{"introduced":"0"},{"fixed":"1.4.5"}]}]

References

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