Cisco IOS vulnerabilities: known CVEs & security history
Cisco · Network / Security · 615 tracked CVEs · 38 actively exploited · updated June 2026 · what is a CVE? →
This is the full list of known vulnerabilities (CVEs) across all Cisco IOS release lines — 615 in total, with 38 actively exploited in the wild. A CVE here doesn't mean your version is affected — check Cisco IOS's current status and the safe version to run.
Known Cisco IOS CVEs
Actively-exploited and most-severe first. Showing the top 80 of 615. Open any CVE for full details.
| CVE | Severity | CVSS | EPSS | Year |
|---|---|---|---|---|
| CVE-2018-0171⚡ exploited | critical | 9.8 | 100% | 2018 |
| CVE-2017-12240⚡ exploited | critical | 9.8 | 14% | 2017 |
| CVE-2017-3881⚡ exploited | critical | 9.8 | 99% | 2017 |
| CVE-2018-0167⚡ exploited | high | 8.8 | 3% | 2018 |
| CVE-2017-6744⚡ exploited | high | 8.8 | 7% | 2017 |
| CVE-2017-6743⚡ exploited | high | 8.8 | 11% | 2017 |
| CVE-2017-6742⚡ exploited | high | 8.8 | 21% | 2017 |
| CVE-2017-6740⚡ exploited | high | 8.8 | 11% | 2017 |
| CVE-2017-6739⚡ exploited | high | 8.8 | 11% | 2017 |
| CVE-2017-6738⚡ exploited | high | 8.8 | 11% | 2017 |
| CVE-2017-6737⚡ exploited | high | 8.8 | 11% | 2017 |
| CVE-2017-6736⚡ exploited | high | 8.8 | 71% | 2017 |
| CVE-2018-0174⚡ exploited | high | 8.6 | 8% | 2018 |
| CVE-2018-0173⚡ exploited | high | 8.6 | 8% | 2018 |
| CVE-2018-0172⚡ exploited | high | 8.6 | 8% | 2018 |
| CVE-2018-0158⚡ exploited | high | 8.6 | 7% | 2018 |
| CVE-2018-0155⚡ exploited | high | 8.6 | 8% | 2018 |
| CVE-2018-0175⚡ exploited | high | 8 | 4% | 2018 |
| CVE-2025-20352⚡ exploited | high | 7.7 | 38% | 2025 |
| CVE-2018-0159⚡ exploited | high | 7.5 | 7% | 2018 |
| CVE-2018-0156⚡ exploited | high | 7.5 | 8% | 2018 |
| CVE-2018-0154⚡ exploited | high | 7.5 | 7% | 2018 |
| CVE-2017-12237⚡ exploited | high | 7.5 | 7% | 2017 |
| CVE-2017-12235⚡ exploited | high | 7.5 | 7% | 2017 |
| CVE-2017-12234⚡ exploited | high | 7.5 | 7% | 2017 |
| CVE-2017-12233⚡ exploited | high | 7.5 | 7% | 2017 |
| CVE-2017-12231⚡ exploited | high | 7.5 | 7% | 2017 |
| CVE-2017-6627⚡ exploited | high | 7.5 | 6% | 2017 |
| CVE-2016-6415⚡ exploited | high | 7.5 | 88% | 2016 |
| CVE-2023-20109⚡ exploited | medium | 6.6 | 2% | 2023 |
| CVE-2017-12238⚡ exploited | medium | 6.5 | 2% | 2017 |
| CVE-2017-12232⚡ exploited | medium | 6.5 | 2% | 2017 |
| CVE-2017-6663⚡ exploited | medium | 6.5 | 2% | 2017 |
| CVE-2018-0161⚡ exploited | medium | 6.3 | 4% | 2018 |
| CVE-2018-0180⚡ exploited | medium | 5.9 | 5% | 2018 |
| CVE-2018-0179⚡ exploited | medium | 5.9 | 5% | 2018 |
| CVE-2017-12319⚡ exploited | medium | 5.9 | 5% | 2018 |
| CVE-2004-1464⚡ exploited | medium | 5.9 | 5% | 2004 |
| CVE-2020-3258 | critical | 9.8 | 5% | 2020 |
| CVE-2020-3198 | critical | 9.8 | 4% | 2020 |
| CVE-2025-20363 | critical | 9 | 8% | 2025 |
| CVE-2011-3271 | high | 10 | 11% | 2011 |
| CVE-2011-0935 | high | 10 | 4% | 2011 |
| CVE-2010-1574 | high | 10 | 5% | 2010 |
| CVE-2010-0581 | high | 10 | 5% | 2010 |
| CVE-2010-0580 | high | 10 | 5% | 2010 |
| CVE-2008-0960 | high | 10 | 69% | 2008 |
| CVE-2006-4950 | high | 10 | 6% | 2006 |
| CVE-2002-1357 | high | 10 | 10% | 2002 |
| CVE-2002-1358 | high | 10 | 6% | 2002 |
| CVE-2002-1359 | high | 10 | 80% | 2002 |
| CVE-2002-1360 | high | 10 | 6% | 2002 |
| CVE-1999-0775 | high | 10 | 3% | 1999 |
| CVE-2015-6280 | high | 9.3 | 4% | 2015 |
| CVE-2011-4012 | high | 9.3 | 1% | 2012 |
| CVE-2008-3807 | high | 9.3 | 4% | 2008 |
| CVE-2008-4128 | high | 9.3 | 12% | 2008 |
| CVE-2007-5552 | high | 9.3 | 3% | 2007 |
| CVE-2007-5381 | high | 9.3 | 15% | 2007 |
| CVE-2007-4286 | high | 9.3 | 19% | 2007 |
| CVE-2007-4292 | high | 9.3 | 3% | 2007 |
| CVE-2007-2586 | high | 9.3 | 14% | 2007 |
| CVE-2006-3291 | high | 9.3 | 4% | 2006 |
| CVE-2005-3481 | high | 9.3 | 7% | 2005 |
| CVE-2003-1398 | high | 9.3 | 2% | 2003 |
| CVE-2001-0537 | high | 9.3 | 67% | 2001 |
| CVE-2015-0635 | high | 9 | 2% | 2015 |
| CVE-2007-4285 | high | 9 | 3% | 2007 |
| CVE-2019-16009 | high | 8.8 | 1% | 2020 |
| CVE-2020-3234 | high | 8.8 | 0% | 2020 |
| CVE-2020-3217 | high | 8.8 | 1% | 2020 |
| CVE-2020-3205 | high | 8.8 | 1% | 2020 |
| CVE-2020-3199 | high | 8.8 | 1% | 2020 |
| CVE-2019-12651 | high | 8.8 | 3% | 2019 |
| CVE-2019-12650 | high | 8.8 | 29% | 2019 |
| CVE-2019-12648 | high | 8.8 | 2% | 2019 |
| CVE-2018-0255 | high | 8.8 | 1% | 2018 |
| CVE-2025-20154 | high | 8.6 | 0% | 2025 |
| CVE-2024-20433 | high | 8.6 | 1% | 2024 |
| CVE-2024-20308 | high | 8.6 | 1% | 2024 |
535 older / lower-severity CVEs not shown — see Cisco IOS's full record.
Is my Cisco IOS version affected?
The list above spans every release. To know whether your version is affected — and the minimum safe version to upgrade to — check it directly.
Check your Cisco IOS version → · Monitor Cisco IOS for new CVEs →
Cisco IOS vulnerabilities — frequently asked
How many known vulnerabilities does Cisco IOS have?
IsItPatched tracks 615 CVEs for Cisco IOS, 38 of which are actively exploited (CISA KEV). 6 are critical-severity and 356 high-severity. These span every release line — what matters is whether the version you run is affected.
Does Cisco IOS have any actively-exploited vulnerabilities?
Yes — 38 Cisco IOS CVEs are in CISA's Known Exploited Vulnerabilities catalog, meaning they are confirmed exploited in the wild. Patch these as a priority.
What is the most severe Cisco IOS vulnerability?
Among tracked issues, CVE-2018-0171 (CRITICAL, CVSS 9.8), which is actively exploited, ranks highest — a Improper input validation weakness.
Is Cisco IOS safe to use?
It depends on the version. The latest supported Cisco IOS release clears the known issues; older versions may still be affected. Check the exact version you run for a verdict.
CVE data aggregated from NVD, CISA KEV and EPSS (FIRST.org). Related: Cisco IOS security status · Cisco IOS end-of-life · actively-exploited CVEs. Always verify against Cisco's advisories — see our disclaimer.