# CVE-2026-55785: free5GC AUSF uses non-constant-time authentication comparisons and logs XRES* in 5G-AKA

> Attackers with log access can read sensitive authentication material, and timing side-channels may theoretically aid bypassing 5G-AKA authentication checks.

- **Severity:** Low 3.7 (`CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 28 Aug 2026
- **Updated:** 31 Aug 2026
- **Also known as:** GHSA-fp46-6vfw-gc9c, GO-2026-6328

## What is CVE-2026-55785?

CVE-2026-55785 is a low-severity vulnerability in free5gc, published on 28 Aug 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

free5GC is an open-source implementation of the 5G core network. Prior to 1.4.5, the AUSF component performs cryptographic authentication comparisons in internal/sbi/processor/ue_authentication.go with ordinary equality helpers. Auth5gAkaComfirmRequestProcedure compares RES* and XRES* with strings.EqualFold and logs the expected XRES* value at INFO level before comparison. EapAuthComfirmRequestProcedure compares AT_MAC and XMAC with bytes.Equal and evaluates XRES == RES with ordinary string equality. These comparisons can return at mismatch-dependent times, although testing did not demonstrate a practical remote timing oracle because of HTTP/SBI timing noise. The INFO log exposes authentication material to operators, log collectors, sidecars, or processes able to read AUSF logs. This issue is fixed in version 1.4.5.

Weakness: CWE-532 (Insertion of Sensitive Information into Log File), CWE-385 (Covert Timing Channel), CWE-208 (Observable Timing Discrepancy)

## Which versions are affected by CVE-2026-55785?

3 open source packages ship an affected version, including github.com/free5gc/ausf.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `github.com/free5gc/ausf` | Go | All versions | 1.4.5 |
| `github.com/free5gc/ausf` | Go | All versions | 1.4.5 |
| `github.com/free5gc/ausf` | Go | All versions | 1.4.5 |

## How do I fix CVE-2026-55785?

Upgrade github.com/free5gc/ausf to 1.4.5 or later.

## Is CVE-2026-55785 being exploited?

There is no known exploitation of CVE-2026-55785 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-55785 and fix it if it is affected.

What it is: CVE-2026-55785 is a low-severity vulnerability in free5gc, published on 28 Aug 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-55785 in the wild and no public exploit code.

Affected packages and fixed versions:
- github.com/free5gc/ausf (Go): affected all versions; fixed in 1.4.5
- github.com/free5gc/ausf (Go): affected all versions; fixed in 1.4.5
- github.com/free5gc/ausf (Go): affected all versions; fixed in 1.4.5

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-55785/ (Markdown: https://insights.sbomify.com/CVE-2026-55785/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-55785
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-55785
- OSV: https://osv.dev/vulnerability/CVE-2026-55785

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-55785/
Summaries are generated and may contain mistakes; the official description above is the record.