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CVE-2021-21293

24
FAUCET Score

CVE-2021-21293 describes an unbounded connection acceptance vulnerability in the blaze Scala library, particularly affecting servers running blaze-core before version 0.14.15 and http4s-blaze-server <= 0.21.16. This flaw allows an attacker to exhaust file handles by continuously accepting connections, even when the service is overloaded. Rated 7.5 HIGH (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H), it can lead to denial of service due to resource exhaustion, with low attack complexity and no authentication required. There is no evidence of active exploitation, public exploit code, or significant community discussion surrounding this vulnerability.

Impacted Technologies

VendorProductVersion(s)CPE
< 0.14.15CPE matchmatch criteria
cpe:2.3:a:typelevel:blaze:*:*:*:*:*:*:*:*

CVSS Data

CVSS version used by this source: 3.1

7.5HIGH

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Attack Vector
NETWORK
Attack Complexity
LOW
Privileges Required
NONE
User Interaction
NONE
Scope
UNCHANGED
Confidentiality Impact
NONE
Integrity Impact
NONE
Availability Impact
HIGH
Exploitability Score
3.9
Impact Score
3.6
CvssVersion
3.1

Exploit Intelligence

EPSS Score
2.12%
Probability of exploitation in next 30 days
EPSS Percentile
79.9%
Percentile rank of EPSS score among Peer Group
As of 2026-07-27
Model: v2026.06.15
This CVE's current EPSS score of 0.0212 is in the 64th percentile among its peer group of 51,551 CVEs.

Social Chatter

The average CVE in this peer group has 0.0 Twitter, 0.0 Reddit, 0.1 Bluesky, 0.1 Mastodon, and 0.4 GitHub mentions.

Media Mentions

No media coverage found for this CVE.

The average CVE in this peer group has 0.1 InfoSec Media, 0.0 Vendor Blog, and 0.0 Security Researcher mentions.

Remediation

Patch Available

Vendor Patches (4)

github_advisorypatch availablevia nvd_reference
View patch
mavenpatch availablevia ghsa
Product: org.http4s:blaze-core_2.11Fixed in: 0.14.15
mavenpatch availablevia ghsa
Product: org.http4s:blaze-core_2.12Fixed in: 0.14.15
mavenpatch availablevia ghsa
Product: org.http4s:blaze-core_2.13Fixed in: 0.14.15

Vendor Advisories (1)

mavenGHSA-xmw9-q7x9-j5qchigh

Unbounded connection acceptance leads to file handle exhaustion

Feb 2, 2021

References

github.com / http4s/blaze/commit/4f786177f9fb71ab272f3a5f6c80bca3e5662aa1
PatchThird Party Advisory
github.com / http4s/blaze/security/advisories/GHSA-xmw9-q7x9-j5qc
Third Party Advisory
github.com / http4s/http4s/security/advisories/GHSA-xhv5-w9c5-2r2w
Third Party Advisory