CVE-2025-20352
CVE-2025-20352 is a security flaw in Cisco IOS and IOS XE, the operating system on Cisco’s routers and switches. Someone who already has a way in can use Cisco IOS and IOS XE to run their own code. The US Cybersecurity and Infrastructure Security Agency (CISA) added it to its catalog of flaws known to be used in attacks on 29 Sep 2025.[1]
Cisco IOS and IOS XE is business software or equipment. Most families won’t have it, but attackers break into it to get inside companies, and from there to what those companies hold about their customers, patients and staff. Cisco has published a fix or advice.
Description
CISA calls it a software SNMP denial of service and remote code execution in Cisco IOS and IOS XE. In its words: “Cisco IOS and IOS XE contains a stack-based buffer overflow vulnerability in the Simple Network Management Protocol (SNMP) subsystem that could allow for denial of service or remote code execution. A successful exploit could allow a low-privileged attacker to cause the affected system to reload, resulting in a DoS condition, or allow a high-privileged attacker to execute arbitrary code as the root user and obtain full control of the affected system.”[1]
The CVE record adds: “A vulnerability in the Simple Network Management Protocol (SNMP) subsystem of Cisco IOS Software and Cisco IOS XE Software could allow the following: An authenticated, remote attacker with low privileges could cause a denial of service (DoS) condition on an affected device that is running Cisco IOS Software or Cisco IOS XE Software. To cause the DoS, the attacker must have the SNMPv2c or earlier read-only community string or valid SNMPv3 user credentials. An authenticated, remote attacker with high privileges could execute code as the root user on an affected device that is running Cisco IOS XE Software. To execute code as the root user, the attacker must have the SNMPv1 or v2c read-only community string or valid SNMPv3 user credentials and administrative or privilege 15 credentials on the affected device. An attacker could exploit this vulnerability by…”[2]
The underlying weakness is stack buffer overflow (CWE-121), in MITRE’s list of common software weaknesses.
It scores 7.7 out of 10 on the Common Vulnerability Scoring System, which rates it high, scored by the organisation that published the CVE using CVSS 3.1.[2]
Affected versions
NVD’s record doesn’t list version ranges for it; Cisco’s advisory has them[3]. CISA names the product as Cisco IOS and IOS XE.
Most families won’t have Cisco IOS and IOS XE; it’s for whoever looks after IT at work.
Exploitation
CISA added it to its catalog of known exploited vulnerabilities on 29 Sep 2025, 5 days after it was made public. CISA lists a flaw only when it has reliable evidence of it being exploited, and gave US federal agencies until 20 Oct 2025 to fix it.[1]
FIRST’s Exploit Prediction Scoring System, which estimates how likely a flaw is to be used in attacks in the next 30 days from what it sees across the internet, puts it at 42%. That’s in the top 2% of the flaws it scores.[4]
CISA assesses it as not automatable: each attack takes some work.
CISA doesn’t say who was attacked, or how.
Fix
Cisco has published a fix or advice.[3] CISA’s required action: “Apply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable.”[1]
- Check whether you use it.Cisco IOS and IOS XE is business software or equipment, so most families won’t have it. If you run a business, or work from home on company equipment, ask whoever looks after your IT.
- Send this page to your IT person.Ask them to confirm it’s fixed, or not in use. CISA gave US government agencies until 20 Oct 2025 to fix it.
- If it can’t be fixed, take it offline.CISA’s advice when there’s no fix is to stop using the product, or take it off the internet, until there is one.
You can’t fix someone else’s server, but you can watch for what follows a break-in like this: a breach notice, a password reset you didn’t ask for, or a scam message that knows things it shouldn’t. HARD watches for those for you and your family.
Timeline
| Date | Event |
|---|---|
| The flaw is made public in the National Vulnerability Database, with a severity score of 7.7.[2] | |
| CISA adds it to its catalog of flaws known to be used in attacks.[1] | |
| CISA’s deadline for US government agencies to fix it.[1] | |
| FIRST puts the odds of it being used in attacks in the next 30 days at 42%.[4] |
See also
Other Cisco IOS and IOS XE flaws
- CVE-2023-20109: group encrypted transport VPN out-of-bounds write ·
- CVE-2017-3881: remote code execution ·
- CVE-2018-0171: software smart install remote code execution ·
Other Cisco flaws
- CVE-2026-76418, Cisco Secure Firewall ASA Software and Cisco Secure FTD Software: unchecked return value to NULL pointer dereference ·
- CVE-2026-76519, Cisco Secure Email Gateway: relative path traversal ·
- CVE-2026-76504, Cisco Catalyst SD-WAN Manager: hex encoding ·
- CVE-2026-76460, Cisco Identity Services Engine: incorrect use of privileged APIs ·
- CVE-2026-76461, Cisco Secure Email Gateway: SQL injection ·
Other stack buffer overflow flaws
- CVE-2026-7273, Zyxel GS1900 Series Switches: stack-based buffer overflow ·
- CVE-2021-27137, DD-WRT: stack-based buffer overflow ·
- CVE-2025-53521, F5 BIG-IP: stack-based buffer overflow ·
- CVE-2025-42599, Qualitia Active! Mail: stack-based buffer overflow ·
- CVE-2025-22457, Ivanti Connect Secure, Policy Secure, and ZTA Gateways: stack-based buffer overflow ·
Added the same day
- CVE-2025-59689, Libraesva Email Security Gateway: command injection ·
- CVE-2025-32463, Sudo: inclusion of functionality from untrusted control sphere ·
- CVE-2025-10035, Fortra GoAnywhere MFT: deserialization of untrusted data ·
- CVE-2021-21311, Adminer: server-side request forgery ·
Every Cisco flaw on CISA’s list · Everything added in September 2025
References
- ^ Cybersecurity and Infrastructure Security Agency. “Cisco IOS and IOS XE Software SNMP Denial of Service and Remote Code Execution Vulnerability”. Known Exploited Vulnerabilities Catalog, added 29 Sep 2025.
- ^ National Institute of Standards and Technology. “CVE-2025-20352 Detail”. National Vulnerability Database, published 24 Sep 2025.
- ^ Cisco. Advisories and fixes: sec.cloudapps.cisco.com.
- ^ FIRST. “Exploit Prediction Scoring System”. EPSS 0.415, percentile 98.7, 31 Oct 2026.
- CVE Program. “CVE-2025-20352”. The official CVE record.
This article is built from CISA’s catalog (version 2026.10.30), NVD’s record and FIRST’s scores, kept in HARD’s database and checked every morning. The plain English is HARD’s.