Cisco IOS XE Software SNMP Denial of Service Vulnerability

highCVE-2026-20124

A vulnerability in the Simple Network Management Protocol (SNMP) subsystem of Cisco IOS XE Software could allow an authenticated, remote attacker to cause an affected device to reload, resulting in a denial of service (DoS) condition. This vulnerability is due to improper error handling when parsing SNMP requests. This vulnerability affects all versions of SNMP — Versions 1, 2c, and 3. An attacker could exploit this vulnerability by sending a malformed SNMP request to an affected device. A successful exploit could allow the attacker to cause the device to reload unexpectedly. The attacker must have the SNMPv1 or v2c read-only or read-write community string or valid SNMPv3 user credentials on the affected device. Cisco has released software updates that address this vulnerability. There are no workarounds that address this vulnerability. There is a mitigation that addresses this vulnerability. This advisory is available at the following link: https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-iosxe-snmp-dos-ZAqNm4MD Security Impact Rating: High CVE: CVE-2026-20124

CSIRTS triage

vendor: Cisco product: IOS XE Software Denial of service

What: Improper error handling in the SNMP subsystem when parsing malformed SNMP requests causes device reload.
Who is affected: Devices with SNMP enabled (all versions 1, 2c, and 3) and accessible to authenticated attackers with SNMP credentials.
Urgency: High severity; denial of service through device reload; requires SNMP community string or SNMPv3 credentials.
Action: Apply Cisco IOS XE Software updates; mitigation available (specific details truncated in advisory).

AI-assisted analysis generated from the source advisory — verify against the original.

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Details

Source: Cisco Security Advisories (INTL · vendor-psirt · site)
Severity: high
Published: 2026-08-05
Exploitation: Not in CISA KEV at last sync

Original advisory: https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-iosxe-snmp-dos-ZAqNm4MD?vs_f=Cisco%20Security%20Advisory%26vs_cat=Security%20Intelligence%26vs_type=RSS%26vs_p=Cisco%20IOS%20XE%20Software%20SNMP%20Denial%20of%20Service%20Vulnerability%26vs_k=1

Exploitation outlook

EPSS (FIRST.org) estimates each CVE’s probability of exploitation in the next 30 days — here is the CSIRTS.com read on those numbers.

Low exploitation riskCVE-2026-201240.34% 30-day exploitation probability — currently an unlikely target, but scores change as exploit code circulates. Riskier than 28% of all EPSS-scored CVEs.

Referenced CVEs

CVE	CSIRTS overview	External
CVE-2026-20124	coverage & exploitation status	NVD · CVE.org

Same CVEs, other sources

How other CERTs, PSIRTs and databases cover the vulnerabilities in this advisory.

high[NEW] [high] Cisco IOS XE: Multiple Vulnerabilitiescert-bund
unknownCisco Products Multiple Vulnerabilitieshkcert
unknownMultiple vulnerabilities in Cisco products (August 6, 2026)cert-fr-avis
highCVE-2026-20124: A vulnerability in the Simple Network Management Protocol (SNMP) subsystem of Cisco IOS XE Sof…nvd
criticalCisco Advance Notification for Publication of August 5, 2026, Security Advisoriescisco-psirt

Recent advisories for Cisco IOS XE

A cluster of recent advisories against the same product widens the attack surface — attackers routinely chain freshly published CVEs on one product, so review these together.

unknownMultiple vulnerabilities in Cisco IOS XE (August 25, 2026)cert-fr-avis · 2026-08-25
unknownNCSC-2026-0279 [1.00] [M/H] Vulnerabilities patched in Cisco IOS XE Softwarencsc-nl · 2026-08-07
high[NEW] [high] Cisco IOS XE: Multiple Vulnerabilitiescert-bund · 2026-08-06
mediumCVE-2026-20311: A vulnerability in the web-based management interface of Cisco IOS XE Software could allow an …nvd · 2026-08-05
mediumCVE-2026-20308: A vulnerability in the web-based management interface of Cisco IOS XE Software could allow an …nvd · 2026-08-05
highCVE-2026-20301: A vulnerability in the Extensible Messaging Client Protocol (XMCP), also referred to as the Ex…nvd · 2026-08-05