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CVE-2024-20439

From Exploited flaws, HARD’s guide to the flaws being used in attacks · Checked
This article is about a flaw in Cisco Smart Licensing Utility. For every flaw being used in attacks, see Exploited flaws; for Cisco’s, see Cisco flaws being used in attacks.

CVE-2024-20439 is a security flaw in Cisco Smart Licensing Utility, Cisco’s business networking equipment. Attackers can use Cisco Smart Licensing Utility to take full control of the machine from anywhere, without logging in. The US Cybersecurity and Infrastructure Security Agency (CISA) added it to its catalog of flaws known to be used in attacks on 31 Mar 2025.[1]

Cisco Smart Licensing Utility 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 static credential in Cisco Smart Licensing Utility. In its words: “Cisco Smart Licensing Utility contains a static credential vulnerability that allows an unauthenticated, remote attacker to log in to an affected system and gain administrative credentials.”[1]

The CVE record adds: “A vulnerability in Cisco Smart Licensing Utility (CSLU) could allow an unauthenticated, remote attacker to log into an affected system by using a static administrative credential. This vulnerability is due to an undocumented static user credential for an administrative account. An attacker could exploit this vulnerability by using the static credentials to login to the affected system. A successful exploit could allow the attacker to login to the affected system with administrative rights over the CSLU application API.”[2]

The underlying weakness is CWE-912, in MITRE’s list of common software weaknesses.

It scores 9.8 out of 10 on the Common Vulnerability Scoring System, which rates it critical, scored by NVD 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 Smart Licensing Utility.

Most families won’t have Cisco Smart Licensing Utility; it’s for whoever looks after IT at work.

Exploitation

CISA added it to its catalog of known exploited vulnerabilities on 31 Mar 2025, 208 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 21 Apr 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 97%. That’s in the top 1% of the flaws it scores.[4]

CISA assesses it as automatable: attackers can run it against many targets at once.

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]

  1. Check whether you use it.Cisco Smart Licensing Utility 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.
  2. Send this page to your IT person.Ask them to confirm it’s fixed, or not in use. CISA gave US government agencies until 21 Apr 2025 to fix it.
  3. 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

DateEvent
The flaw is made public in the National Vulnerability Database, with a severity score of 9.8.[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 97%.[4]

See also

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 ·

Similar flaws

Every Cisco flaw on CISA’s list · Everything added in March 2025

References

  1. ^ Cybersecurity and Infrastructure Security Agency. “Cisco Smart Licensing Utility Static Credential Vulnerability”. Known Exploited Vulnerabilities Catalog, added 31 Mar 2025.
  2. ^ National Institute of Standards and Technology. “CVE-2024-20439 Detail”. National Vulnerability Database, published 4 Sep 2024.
  3. ^ Cisco. Advisories and fixes: sec.cloudapps.cisco.com.
  4. ^ FIRST. “Exploit Prediction Scoring System”. EPSS 0.971, percentile 99.9, 31 Oct 2026.
  5. CVE Program. “CVE-2024-20439”. 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.