GHSA-xmw9-q7x9-j5qc · Severity: high · Ecosystem: maven — Unbounded connection acceptance leads to file handle exhaustion
blaze is a Scala library for building asynchronous pipelines, with a focus on network IO. All servers running blaze-core before version 0.14.15 are affected by a vulnerability in which unbounded connection acceptance leads to file handle exhaustion. Blaze, accepts connections unconditionally on a dedicated thread pool. This has the net effect of amplifying degradation in services that are unable to handle their current request load, since incoming connections are still accepted and added to an unbounded queue. Each connection allocates a socket handle, which drains a scarce OS resource. This can also confound higher level circuit breakers which work based on detecting failed connections. The vast majority of affected users are using it as part of http4s-blaze-server <= 0.21.16. http4s provides a mechanism for limiting open connections, but is enforced inside the Blaze accept loop, after the connection is accepted and the socket opened. Thus, the limit only prevents the number of connections which can be simultaneously processed, not the number of connections which can be held open. The issue is fixed in version 0.14.15 for "NIO1SocketServerGroup". A "maxConnections" parameter is added, with a default value of 512. Concurrent connections beyond this limit are rejected. To run unbounded, which is not recommended, set a negative number. The "NIO2SocketServerGroup" has no such setting and is now deprecated. There are several possible workarounds described in the refrenced GitHub Advisory GHSA-xmw9-q7x9-j5qc.
Conclusion & alert: CVE-2021-21293 is rated Moderate Risk (59.5/100): CVSS High severity, with medium exploitation likelihood (EPSS 2.12%). Core evidence: EPSS rose +1.71% over the last day, indicating growing attacker interest. Mandatory action: Review affected assets and schedule remediation.
Risk is dynamic; we continuously reassess and refresh what is shown on this page as upstream context changes.
EPSS lead: Daily EPSS estimates relative likelihood of exploitation; percentile ranks this CVE among scored vulnerabilities (higher = more severe relative rank).
| # | Date | Old EPSS score | New EPSS score | Delta (New - Old) |
|---|---|---|---|---|
| 1 | 2026-06-15 | 0.41% | 2.12% | +1.71% |
| 2 | 2025-07-20 | 0.53% | 0.41% | -0.12% |
| 3 | 2025-03-30 | — | 0.53% | — |
Full EPSS history (11 records total)
CVSS metrics for this CVE.
| Base score | Version | Severity | Vector | Exploitability | Impact | Score source |
|---|---|---|---|---|---|---|
| 7.5 | 3.1 | HIGH |
|
3.9 | 3.6 | [email protected] |
| 7.5 | 3.1 | HIGH |
|
3.9 | 3.6 | [email protected] |
| 5.0 | 2.0 | MEDIUM |
|
10.0 | 2.9 | [email protected] |
GHSA-xmw9-q7x9-j5qc · Severity: high · Ecosystem: maven — Unbounded connection acceptance leads to file handle exhaustion
| URL | Tags |
|---|---|
| https://github.com/http4s/blaze/commit/4f786177f9fb71ab272f3a5f6c80bca3e5662aa1 | Patch Third Party Advisory |
| https://github.com/http4s/blaze/security/advisories/GHSA-xmw9-q7x9-j5qc | Third Party Advisory |
| https://github.com/http4s/http4s/security/advisories/GHSA-xhv5-w9c5-2r2w | Third Party Advisory |