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What is CVE-2021-45046?A critical-severity flaw criminals are using now.

Critical severityKnown exploited55 affected products
The short answer

CVE-2021-45046 is a critical-severity flaw (CVSS 9.0) in Log4j from Apache, published on 14 December 2021. It is on the list of flaws known to be exploited, so criminals are already using it. The latest forecast puts its chance of use in the next 30 days at over 99%. If you run an affected version, patch it first.

Check if it affects you →How to fix it

Published 14 December 2021. Record last updated 27 October 2025. We keep this page's data up to date.

What it does

What is CVE-2021-45046? In plain terms.

It can be attacked from anywhere on the internet without logging in, and nobody has to click anything. If it works, the attacker can read data, change data and take it offline.

The official description

It was found that the fix to address CVE-2021-44228 in Apache Log4j 2.15.0 was incomplete in certain non-default configurations. This could allows attackers with control over Thread Context Map (MDC) input data when the logging configuration uses a non-default Pattern Layout with either a Context Lookup (for example, $${ctx:loginId}) or a Thread Context Map pattern (%X, %mdc, or %MDC) to craft malicious input data using a JNDI Lookup pattern resulting in an information leak and remote code execution in some environments and local code execution in all environments. Log4j 2.16.0 (Java 8) and 2.12.2 (Java 7) fix this issue by removing support for message lookup patterns and disabling JNDI functionality by default.

What kind of flaw is it?

  • CWE-917Improper Neutralization of Special Elements used in an Expression Language Statement ('Expression Language Injection')
CVSS 3.1 scoreCritical · 9.0

How an attack on it works

Read straight from its severity rating, translated out of the shorthand.

  • Where an attacker can beAnywhere on the internet
  • How hard it is to pull offHard: conditions must line up
  • Login needed firstNo login needed
  • Does someone have to clickNo, nobody has to do anything
  • What an attacker getsCan read data, change data and take it offline

Severity vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:H/I:H/A:H

Exploitation

Is CVE-2021-45046 being exploited? Yes.

Attackers are already using it. It is on the government list of flaws known to be exploited, and the latest forecast puts the chance of it being used in the next 30 days at over 99%.

Known to be exploitedYesOn the government list of exploited flaws
Chance of use in the next 30 days>99%Its EPSS score, from the latest forecast

Timeline

  1. Published
  2. Record last updated
How Precursor Intelligence ranks it
90out of 100Critical

CVE-2021-45046 scores 90. Action: Emergency patch.

We keep the score of every published flaw up to date as the evidence changes. Four things go into the score, and evidence that criminals are actually using it counts most. In order:

  • Evidence it is being exploitedBiggest factor
  • How severe it isStrong factor
  • How widely exposed it isSmaller factor
  • Threat activity around itSmaller factor

85 and above is Critical. Anything confirmed as exploited is always marked for an emergency patch, whatever its score.

When CVE-2021-45046 matches software you track, it lands in your list with its score and the reasons behind it.

See your own ranked list →
Affected products

Who is affected by CVE-2021-45046? 55 products.

The published record lists 55 products from 7 vendors. Versions are shown as published: "2.0.1 to before 2.12.2" means from 2.0.1 up to, but not including, 2.12.2. If you run one of these, check your version, then go to the fix below.

Remediation

How do I fix CVE-2021-45046? Four steps.

  1. Check whether you run itCompare your versions with the affected products above. Not sure what you run? Precursor Intelligence can work it out from your public website, or you can pick it from a list.
  2. Apply the vendor’s fixInstall the update named in the vendor’s advisory. We’ve put the advisories and patch notes first in the list.
  3. If you can’t patch todayFollow any mitigation the vendor publishes, and limit who can reach the affected system from the internet until the update is in.
  4. Check it wasn’t used before you patchedBecause criminals are already using this flaw, look for signs of a break-in on affected systems using the vendor’s guidance.

References

22 links
Precursor Intelligence

Does CVE-2021-45046 affect you? We'll keep checking.

Looking flaws up one at a time doesn't scale. Tell us what you run once, and we tell you which flaws matter to you, in what order, and keep watching for new ones.

  1. Tell us what you runPick your software from a list, or let us work it out from your website.
  2. We match it to every flawOver 400,000 published flaws, checked against your list.
  3. Ranked by real-world riskA 0 to 100 score, led by evidence criminals are using it.
  4. Told as soon as we knowAn alert by email, in the app or by webhook to your own tools.
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FAQ

Common questions, answered plainly.

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CVE-2021-45046 is a critical-severity flaw in Log4j from Apache, published on 14 December 2021. It can be attacked from anywhere on the internet without logging in, and nobody has to click anything. If it works, the attacker can read data, change data and take it offline.

It scores 9.0 out of 10 on the CVSS severity scale, which is critical. Our risk score for CVE-2021-45046 is 90 out of 100, which is Critical. Its action is "Emergency patch". Attackers are using this flaw today. If you run an affected version, it goes to the top of your list.

Attackers are already using it. It is on the government list of flaws known to be exploited, and the latest forecast puts the chance of it being used in the next 30 days at over 99%.

For Log4j from Apache: 2.0-beta9, 2.0-rc1, 2.0-rc2, 2.0, 2.0.1 to before 2.12.2, 2.13.0 to before 2.16.0. The record lists 55 products in all, each with its versions, under "Who is affected" on this page.

Install the update the vendor names in its advisory, linked first under "How do I fix" on this page. If you can't patch today, follow the vendor's mitigation and limit who can reach the affected system from the internet. Because criminals are already using it, also check affected systems for signs of a break-in.

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