CVE-2021-1356

MEDIUMNVD 4.34.3—
EchelonGraph scoreMEDIUM confidence

This medium-severity CVE scores 4.3 under NVD CVSS v3. EPSS exploit probability: 0.1%, top 71% of all CVEs by exploit prediction. GitHub Security Advisory data not yet ingested — confidence will rise once GHSA publishes (typical lag: hours to days for open-source ecosystem CVEs; never for infrastructure-only CVEs).

Triggered by: NVD CVSS baseline
Sources: epss, nvd
4.3
EchelonGraph verdictMonitorLow exploitation likelihood right now — keep watching.
  • Lower severity and no public exploit yet
CISA-KEV: Not listedEPSS: 1%CVSS: 4.3Exploit: NoneExposed: 0

No vendor fix yet — apply a workaround or compensating control (WAF / firewall / segmentation) and watch for a patch.

Multiple vulnerabilities in the web UI of Cisco IOS XE Software could allow an authenticated, remote attacker with read-only privileges to cause the web UI software to become unresponsive and consume vty line instances, resulting in a denial of service (DoS) condition. These vulnerabilities are due to insufficient error handling in the web UI. An attacker could exploit these vulnerabilities by sending crafted HTTP packets to an affected device. A successful exploit could allow the attacker to cause the web UI software to become unresponsive and consume all available vty lines, preventing new session establishment and resulting in a DoS condition. Manual intervention would be required to regain web UI and vty session functionality. Note: These vulnerabilities do not affect the console connection.

CVSS v3
4.3
EG Score
4.3(medium)
EPSS
57.1%
KEV
Not listed

Published

March 24, 2021

Last Modified

November 21, 2024

References (2)

Weakness Classification(2)

MITRE Common Weakness Enumeration — the root-cause categories this CVE belongs to.

Data Freshness Timeline

(refreshed 8× in last 7d / 46× in last 30d)

Each row is a source pipeline that fetched or updated this CVE on that date, with what changed. For example, "NVD update" means NVD published or revised its analysis for this CVE; "MITRE cvelistV5" means we ingested or refreshed it from the CNA feed. Most recent first.

  1. 2026-07-20 17:04 UTCEPSS rescore
  2. 2026-07-19 14:28 UTCEPSS rescore
  3. 2026-07-19 02:26 UTCEPSS rescore
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  1. 2026-07-02 16:57 UTCEPSS rescore
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  3. 2026-06-30 23:20 UTCEPSS rescore
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  26. 2026-06-18 17:51 UTCEPSS rescore
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  41. 2026-06-07 15:23 UTCEPSS rescore
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  43. 2026-06-06 13:46 UTCEPSS rescore
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  46. 2026-06-05 22:45 UTCEPSS rescore
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  48. 2026-06-05 06:09 UTCEPSS rescore
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  63. 2026-05-27 13:39 UTCEPSS rescore
  64. 2026-05-26 19:13 UTCEG score recompute
  65. 2026-05-26 19:13 UTCGHSA enrichment
  66. 2026-05-26 13:42 UTCEPSS rescore
  67. 2026-05-26 13:42 UTCEPSS rescore
  68. 2026-05-26 07:17 UTCEPSS rescore
  69. 2026-05-26 07:17 UTCEPSS rescore
  70. 2026-05-25 10:46 UTCOSV refresh
  71. 2026-05-24 16:49 UTCEPSS rescore

Related CVEs(same CWE)

Frequently asked(5)

What is CVE-2021-1356?
CVE-2021-1356 is a medium vulnerability published on March 24, 2021. Multiple vulnerabilities in the web UI of Cisco IOS XE Software could allow an authenticated, remote attacker with read-only privileges to cause the web UI software to become unresponsive and consume vty line instances, resulting in a denial of service (DoS) condition. These vulnerabilities are due…
When was CVE-2021-1356 disclosed?
CVE-2021-1356 was first published in the National Vulnerability Database on March 24, 2021, with the most recent update on November 21, 2024. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
Is CVE-2021-1356 actively exploited?
CVE-2021-1356 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 57.1% percentile likelihood of exploitation in the next 30 days — higher percentiles indicate greater predicted risk.
What is the CVSS score of CVE-2021-1356?
CVE-2021-1356 has a CVSS v3 base score of 4.3 (NVD).
How do I remediate CVE-2021-1356?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2021-1356, EchelonGraph cross-links them in the Vendor Advisories panel below — those typically contain the canonical remediation steps, fixed version numbers, and any vendor-specific mitigations.

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