vulnerability / NVI-00013788 / Revision 1
free5GC AUSF uses non-constant-time authentication comparisons and logs XRES* in 5G-AKA
GitHub lists this reviewed advisory for github.com/free5gc/ausf. Published version ranges and source prerequisites are shown below; this is not an inspection of a visitor’s application.
This report has not inspected your inventory, configuration, deployed build, reachability or evidence. A catalog listing and a severity score do not establish exposure or compromise.
01 / Meaning
Why it matters
Published affected context helps an owner decide what evidence to gather. This report has not examined your application.
3.7 low
GitHub source severity; exploitability and local consequence require separate evidence.
As of · GitHub Advisory Database
02 / Applicability
The affected context
Affected versions, configuration prerequisites and known exclusions are public. Confirm each one against the deployed service.
github.com/free5gc/ausf
source listed< 1.4.5
### 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. ###
03 / Response
What to do next
- investigate
Identify the exact component and deployed version, examine the linked publisher’s conditions, and retain evidence of any mitigation.
Confirm current vendor support, compatibility and deployment evidence. This report has not tested a fix in your system. GitHub Advisory Database
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04 / Limits
What this report cannot establish
- Customer inventory, deployment, reachability and exploitation have not been inspected.
05 / Provenance
Sources you can inspect
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- GHSA-fp46-6vfw-gc9c ↗
GitHub Advisory Database · vendor advisory
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Public revision history
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- Revision 1 ·
First indexed by Null; source disclosure date is shown separately.