CVE-2021-30639
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DoS after non-blocking IO error
rank 28 = 2 + 19 + 0 + 7 + 0
rank@v1 · scheduled
Someone is already using it
CISA KEV catalog · public proof-of-concept · FIRST EPSS
EPSS 0.06889 · without this subject the record ranks 26
What it costs you if it fires
NVD CVSS base score, then the CNA's own
CVSS 7.5, from NVD · without this subject the record ranks 9
It is getting worse, not staying still
FIRST EPSS series, rescorings and bad loads removed
no persisting rise in 365 days · without this subject the record ranks 28
How much of the world it touches
NVD CPE configurations
7 products in the CPE ranges · without this subject the record ranks 21
Someone else already set the date
CISA KEV remediation due date
no CISA due date · without this subject the record ranks 28
$210,000 = $4.99M incident cost x 0.6121449559255632 exposure x 0.06889 likelihood
udv@v1 · unaudited · wrong for you until you say what you run
$4.99M is the cost of a breach that happened, from IBM Cost of a Data Breach Report 2026, global average. It is not the value of any asset of yours. That average already covers breaches of every severity, so scaling it by exposure understates a partial-impact record. That is an assumption, not a measurement. Your own asset value goes in the decision record.
Hindsight · the state
Foresight · where to check next
This record is one instance of CWE-755, improper handling of exceptional conditions. The index holds 594 prior instances of this class, 5 KEV-listed. The nearest of its KEV-listed records are drawn beside this. taxonomy@v1
Running Apache Tomcat? Check your version
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Harm, if it fires from the vector and the weakness
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CISA KEV & Federal Remediation Deadline from the record and CISA
The fix, and how long it's been waiting.
Exploit Status & Known PoCs a ladder, not a score
Current rung: Nothing observed in held sources.
- RUNG 1Nothing observed in held sources
- RUNG 2Proof-of-concept published
- RUNG 3Exploited in the wild · CISA KEV listed
- RUNG 4Ransomware campaign use known
Affected & Fixed Versions as published
Show all 7 published ranges
A rung lights from a row in the index, never from an assessment. "Held sources" is the true scope of the claim: this index reads the CVE record, NVD, CISA KEV, FIRST's EPSS and public proof-of-concept repositories, and it does not observe attacks.
What it is stated by the CNA
A vulnerability in Apache Tomcat allows an attacker to remotely trigger a denial of service. An error introduced as part of a change to improve error handling during non-blocking I/O meant that the error flag associated with the Request object was not reset between requests. This meant that once a non-blocking I/O error occurred, all future requests handled by that request object would fail. Users were able to trigger non-blocking I/O errors, e.g. by dropping a connection, thereby creating the possibility of triggering a DoS. Applications that do not use non-blocking I/O are not exposed to this vulnerability. This issue affects Apache Tomcat 10.0.3 to 10.0.4; 9.0.44; 8.5.64. receipt
NVD's analysis a second authority
- severity
- 7.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
- weakness
- CWE-755
- affected versions
- apache tomcat 8.5.64; apache tomcat 9.0.44; apache tomcat 10.0.3; and 4 more, listed in full below
check it yourself lists.apache.org lists.apache.org lists.apache.org security.netapp.com kc.mcafee.com oracle.com +1 morereceipt
Dated events
Movement the material steps
This score more than doubled inside 72 hours. Both observations are in the full history below.
Show all 37 observations
37 observations held. A highlighted step crossed a promotion threshold. A step marked with a scoring model moved because the instrument was replaced, not because the vulnerability changed. receipt
The full biography
Exploit probability more than doubled between 2021-07-13 and 2021-07-16 (0.01036 → 0.03053) and the record had been public for 4 years, 11 months when this index was last written.
The pattern, elsewhere
This record is one instance of CWE-755, improper handling of exceptional conditions. The index holds 594 prior instances of this class, 5 KEV-listed. The nearest of its KEV-listed records are drawn beside this. [email protected]
"Matches n of m" counts the attributes the two records can both be compared on: the CVSS metrics they share a version of, any weakness class beyond this one, and the vendor. fit-rules@v1
594 records in this class held. The six above are drawn from the ones CISA has listed as exploited, ranked by how much of the record matches this one. That is why every one of them is KEV-listed: the pool is, so the colour on those spokes says nothing the pool has not already said.
No curated product neighbourhood is held for this product, so the records above are the nearest this index can name. The neighbourhood table covers a small set of products and is extended by hand.
Siblings and hubs
Records related to this one
No record cites this identifier and it carries no alias. Its defect family is below.
Its defect family
apache software foundation apache tomcat
Grouped by shared product and weakness, not by shared vulnerability. Each record's own state is on its own page.
Family membership: held values
Nothing we hold separates this record from the others in its defect family. This page is kept and dated, and the defect family's own page is the one we offer for indexing: the whole group.
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What usually comes next
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