Description
Net-SNMP through 5.9.5.2 contains a denial of service vulnerability in the SMUX module where smux_accept() performs an unauthenticated blocking read without timeout on newly accepted connections. An unauthenticated remote client can connect to the SMUX listener and send no data, causing the single-threaded snmpd main loop to block indefinitely and suspend all SNMP processing.
Affected products
| Vendor | Product | Affected | Fixed |
|---|---|---|---|
| net-snmp | Net-SNMP | ≤ 5.9.5.2 | — |
Fixed in Linux distributions
Distributions backport fixes, so the version that fixes this vulnerability differs per release — upgrade to at least the version shown. From the distributions' security trackers and advisories.
Debian
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Debian 14 | net-snmp | 5.9.5.2+dfsg-3 | — |
| Debian 13 | net-snmp | No fix yet | — |
| Debian 12 | net-snmp | No fix yet | — |
Ubuntu
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Ubuntu 26.04 LTS | net-snmp | 5.9.4+dfsg-2ubuntu3.1 | USN-8997-1 |
| Ubuntu 24.04 LTS | net-snmp | 5.9.4+dfsg-1.1ubuntu3.3 | USN-8997-1 |
| Ubuntu 22.04 LTS | net-snmp | 5.9.1+dfsg-1ubuntu2.10 | USN-8997-1 |
Show 4 more (older releases, extended support, other products)Fewer releases
| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Ubuntu Pro 20.04 LTS | net-snmp | No fix yet | — |
| Ubuntu Pro 18.04 LTS | net-snmp | No fix yet | — |
| Ubuntu Pro 16.04 LTS | net-snmp | No fix yet | — |
| Ubuntu Pro 14.04 LTS | net-snmp | No fix yet | — |
Azure Linux
| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Azure Linux 3 | net-snmp | No fix yet | — |
Wolfi
| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Wolfi rolling | net-snmp +7 | No fix yet | — |
Advisories 2
- USN-8997-1 net-snmp vulnerability Ubuntu Security Notices (USN) · Nov 5, 2026
- WID-SEC-2026-3341 Net-SNMP: Schwachstelle ermöglicht Denial of Service BSI CERT-Bund (WID) · Nov 4, 2026
References
- Unauthenticated remote denial of service in Net-SNMP snmpd via blocking pre-authentication SMUX read third-party-advisory
- agent/mibgroup/smux/smux.c at v5.9.5.2 technical-description
- Product product
- VulnCheck Advisory: Net-SNMP through 5.9.5.2 Denial of Service via Blocking Unauthenticated SMUX Read third-party-advisory