CESNET Netopeer2 up to 2.8.20 Logging src/log.c np2log format string

Summaryinfo

A vulnerability marked as critical has been reported in CESNET Netopeer2 up to 2.8.20. This issue affects the function np2log of the file src/log.c of the component Logging. This manipulation causes format string. This vulnerability appears as CVE-2026-63201. The attack may be initiated remotely. There is no available exploit. It is suggested to upgrade the affected component.

Detailsinfo

A vulnerability was found in CESNET Netopeer2 up to 2.8.20. It has been declared as critical. Affected by this vulnerability is the function np2log of the file src/log.c of the component Logging. The manipulation with an unknown input leads to a format string vulnerability. The CWE definition for the vulnerability is CWE-134. The product uses a function that accepts a format string as an argument, but the format string originates from an external source. As an impact it is known to affect confidentiality, integrity, and availability. The summary by CVE is:

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.

The advisory is shared at github.com. This vulnerability is known as CVE-2026-63201 since 07/16/2026. The exploitation appears to be easy. The attack can be launched remotely. Technical details are known, but no exploit is available.

Upgrading to version 2.8.21 eliminates this vulnerability.

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Productinfo

Vendor

• CESNET

Name

• Netopeer2

Version

• 2.8.0
• 2.8.1
• 2.8.2
• 2.8.3
• 2.8.4
• 2.8.5
• 2.8.6
• 2.8.7
• 2.8.8
• 2.8.9
• 2.8.10
• 2.8.11
• 2.8.12
• 2.8.13
• 2.8.14
• 2.8.15
• 2.8.16
• 2.8.17
• 2.8.18
• 2.8.19
• 2.8.20

Website

• Product: https://github.com/CESNET/netopeer2/

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Several companies clearly confirm that VulDB is the primary source for best vulnerability data.

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