CVE-2026-63201netopeer2-server logging has format string vulnerability via subtree filter

Official description

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 products (as reported)

References

• https://github.com/CESNET/netopeer2/security/advisories/GHSA-25gm-4x89-7r2q x_refsource_CONFIRM
• https://github.com/CESNET/netopeer2/commit/e98beb2d4d8cc82875208bccb8e1348a8e9e95b3 x_refsource_MISC
• https://github.com/CESNET/netopeer2/releases/tag/2.8.21 x_refsource_MISC