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CVE Record

CVE-2021-31810: An issue was discovered in Ruby through 2.6.7, 2.7.x through 2.7.3, and 3.x through 3.0.1.

An issue was discovered in Ruby through 2.6.7, 2.7.x through 2.7.3, and 3.x through 3.0.1. A malicious FTP server can use the PASV response to trick Net::FTP into connecting back to a given IP address and port. This potentially makes curl extract information about services that are otherwise private and not disclosed (e.g., the attacker can conduct port scans and service banner extractions).

UnknownCVSS not scoredNot KEV-listedUpdated
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Glexia's TakeAutomated analysismoderate

Security readout for executives and security teams

Plain-English summary

This flaw affects Ruby’s Net::FTP library. A malicious FTP server can misdirect a Ruby client into connecting to another IP address and port, potentially exposing information about internal services the attacker could not otherwise see.

Executive priority

Treat this as a targeted exposure-reduction issue, not a confirmed emergency. Prioritize systems where Ruby FTP clients can reach sensitive internal networks or where users can influence FTP destinations.

Technical view

Ruby Net::FTP trusted server-supplied PASV connection details in affected Ruby releases through 2.6.7, 2.7.3, and 3.0.1. The result is an FTP bounce-style issue that can enable private service probing or banner exposure through the client’s network position.

Likely exposure

Exposure is most likely in Ruby applications or services that use Net::FTP to connect to FTP servers, especially externally supplied or untrusted servers. Packaged Ruby, JRuby, and vendor products may also inherit risk through bundled runtimes.

Exploitation context

The bundle does not show CISA KEV listing or active exploitation evidence. Abuse requires controlling or influencing the FTP server a vulnerable Ruby client contacts, then using the client’s network reachability to probe other services.

Researcher notes

The source bundle lacks CVSS, CWE, and detailed product CPEs. The core risk is trust of PASV response host and port data in Net::FTP, enabling indirect internal probing from the client environment.

Mitigation direction

  • Update Ruby or packaged Ruby using Ruby and distribution vendor advisories.
  • Move beyond listed affected Ruby ranges: 2.6.7, 2.7.3, and 3.0.1.
  • Apply JRuby, Fedora, Debian, Gentoo, Oracle, and NetApp updates where relevant.
  • Restrict FTP use to trusted servers where business workflows still require FTP.
  • Limit egress from Ruby services to approved destinations and ports.

Validation and detection

  • Inventory applications using Ruby Net::FTP or FTP client workflows.
  • Check deployed Ruby and JRuby versions against listed affected ranges.
  • Review operating system package advisories for backported Ruby fixes.
  • Identify services that connect to user-controlled or third-party FTP servers.
  • Verify egress controls reduce access to internal-only services.
Prepared
Confidence
medium
Sources
10

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

These mappings and lookup hints may be relevant to the vulnerability behavior, CWE, affected product, or exposure path. Glexia-inferred context is not an official MITRE, ATT&CK, CWE, or CVE Program mapping.

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CVE-2021-31810 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
9Source 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

CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.