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CVE Record

CVE-2021-39240: An issue was discovered in HAProxy 2.2 before 2.2.16, 2.3 before 2.3.13, and 2.4 before 2.4.3.

An issue was discovered in HAProxy 2.2 before 2.2.16, 2.3 before 2.3.13, and 2.4 before 2.4.3. It does not ensure that the scheme and path portions of a URI have the expected characters. For example, the authority field (as observed on a target HTTP/2 server) might differ from what the routing rules were intended to achieve.

UnknownCVSS not scoredNot KEV-listedUpdated
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Glexia's TakeAutomated analysismoderate

Security readout for executives and security teams

Plain-English summary

HAProxy versions before the listed fixed releases may mishandle unusual URI characters, causing routing expectations to differ from what an HTTP/2 backend sees. For organizations using HAProxy as an edge or internal reverse proxy, this can undermine routing assumptions. The public bundle does not provide CVSS, CWE, or confirmed exploitation evidence.

Executive priority

Treat this as a timely proxy hygiene issue. It is not confirmed as exploited in the supplied sources, but HAProxy often sits at important trust boundaries, so affected versions should be updated during normal security maintenance with priority for exposed gateways.

Technical view

The issue affects HAProxy 2.2 before 2.2.16, 2.3 before 2.3.13, and 2.4 before 2.4.3. HAProxy did not ensure scheme and path URI portions contained expected characters, so the authority observed by a target HTTP/2 server could differ from intended routing rules.

Likely exposure

Exposure is most likely where affected HAProxy 2.2, 2.3, or 2.4 builds process HTTP/2 traffic and routing rules depend on URI scheme, path, or authority interpretation.

Exploitation context

The provided sources do not show CISA KEV listing or active exploitation. The risk is request interpretation and routing ambiguity, not a documented remote code execution issue in the supplied evidence.

Researcher notes

Evidence is strongest for affected version ranges and fixed releases. The bundle lacks CVSS, CWE, detailed impact scoring, and exploit confirmation. Analysis should stay focused on URI validation, HTTP/2 authority interpretation, and rule-routing mismatch until vendor material provides more detail.

Mitigation direction

  • Upgrade HAProxy to 2.2.16, 2.3.13, 2.4.3, or later supported releases.
  • Apply Debian or Fedora HAProxy security updates where those distributions manage the package.
  • Check HAProxy vendor guidance for any environment-specific configuration recommendations.
  • Prioritize internet-facing or trust-boundary proxies that handle HTTP/2 traffic.

Validation and detection

  • Inventory HAProxy versions across hosts, containers, appliances, and base images.
  • Confirm whether affected deployments process HTTP/2 traffic toward backend services.
  • Review routing rules that depend on URI scheme, path, host, or authority behavior.
  • Verify patched package versions after distribution security updates are applied.
Prepared
Confidence
medium
Sources
8

Public sources used

Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.

Potential ATT&CK relevance

Conservative CVE-to-ATT&CK context

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CVE-2021-39240 mapping review

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Vulnerability profileCVE Program record
Severity
Unknown
CVSS
Not scored
Known Exploited
No
Published
Official CVE source material

CNA and ADP enrichment extracted from CVE v5

These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.

0CVSS vectors
0Timeline events
0ADP providers
7Source links

CVSS and timeline data

No CVSS vectors or timeline events were available in the normalized CVE source material.

Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
n/an/an/aListed
Weakness

CWE details

No CWE listed

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