---
id: CVE-2026-63201
title: netopeer2-server logging has format string vulnerability via subtree filter
summary: >-
  Netopeer2 is a server for implementing network configuration management based
  on the `NETCONF` Protocol. In affected versions, a low-privileged
  authenticated `NETCONF` user can remotely crash `netopeer2-server` by sending
  a `get RPC` wit…
severity: high
cvss: 7.1
cvssVector: 'CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N'
cvssSource: cna
cwe:
  - CWE-134
vendor: CESNET
product: netopeer2
affected:
  - netopeer2 < 2.8.21
ssvc:
  exploitation: none
  automatable: 'no'
  technicalImpact: partial
  timestamp: '2026-11-02T17:03:24.936130Z'
published: '2026-10-30'
updated: '2026-11-02'
sourceUpdated: '2026-11-02T18:08:38.871Z'
source: CVEORG
sourceUrl: 'https://www.cve.org/CVERecord?id=CVE-2026-63201'
references:
  - url: >-
      https://github.com/CESNET/netopeer2/security/advisories/GHSA-25gm-4x89-7r2q
    label: >-
      https://github.com/CESNET/netopeer2/security/advisories/GHSA-25gm-4x89-7r2q
  - url: >-
      https://github.com/CESNET/netopeer2/commit/e98beb2d4d8cc82875208bccb8e1348a8e9e95b3
    label: >-
      https://github.com/CESNET/netopeer2/commit/e98beb2d4d8cc82875208bccb8e1348a8e9e95b3
  - url: 'https://github.com/CESNET/netopeer2/releases/tag/2.8.21'
    label: 'https://github.com/CESNET/netopeer2/releases/tag/2.8.21'
tags:
  - cve.org
epss: 0.00432
epssPercentile: 0.37774
ingestedAt: '2026-11-05T19:30:42.765Z'
---

## Overview

Netopeer2 is a server for implementing network configuration management based on the `NETCONF` Protocol. In affected versions, a low-privileged authenticated `NETCONF` user can remotely crash `netopeer2-server` by sending a `get RPC` with an invalid `subtree filter` whose text contains format specifiers. In `src/netconf.c`, `np2srv_rpc_get_cb()` sends the invalid value through `ERR()` to `np2log_printf()`, where `vsnprintf()` first formats the message safely. In `src/log.c`, that already formatted buffer is subsequently passed to `np2log()` as the format string itself, causing `vsyslog()` to interpret attacker-controlled percent sequences and read invalid pointer arguments. The reported denial of service was confirmed on version 2.8.7 using `NETCONF`-over-SSH and AddressSanitizer; reliable remote code execution was not confirmed. `The advisory identifies 2.8.8 as patched`; repository comparisons verify the fix in public release 2.8.21. The affected/fixed boundary remains unresolved because no public 2.8.8 tag was located, which does not establish the status of an untagged 2.8.8 build.

## Affected

- `netopeer2 < 2.8.21`

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.