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CVE Record

CVE-2021-33500: PuTTY before 0.75 on Windows allows remote servers to cause a denial of service (Windows GUI hang) by telli...

PuTTY before 0.75 on Windows allows remote servers to cause a denial of service (Windows GUI hang) by telling the PuTTY window to change its title repeatedly at high speed, which results in many SetWindowTextA or SetWindowTextW calls. NOTE: the same attack methodology may affect some OS-level GUIs on Linux or other platforms for similar reasons.

HighCVSS 7.5Not KEV-listedUpdated
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Glexia's TakeAutomated analysismoderate

Security readout for executives and security teams

Plain-English summary

CVE-2021-33500 is a denial-of-service issue in PuTTY before 0.75 on Windows. A remote server can make the PuTTY graphical window hang by forcing rapid title changes. This does not indicate data theft or code execution, but it can interrupt administrator access during operations.

Executive priority

Schedule remediation through endpoint software maintenance, prioritizing administrator workstations. Urgency is lower than code execution vulnerabilities, but outages during remote administration can affect incident response and operations.

Technical view

The issue affects PuTTY before 0.75 on Windows. A server-controlled terminal title update path can trigger excessive Windows SetWindowTextA/SetWindowTextW calls, causing the GUI to hang. The CVSS 3.1 score is 7.5 with availability impact only. Sources note similar methodology may affect some GUI behavior on other platforms.

Likely exposure

Exposure is most likely where Windows users still run PuTTY versions earlier than 0.75, especially administrators connecting to untrusted, compromised, or third-party SSH servers. The source bundle does not identify specific packaged downstream products or enterprise distributions.

Exploitation context

The source bundle includes public references describing the behavior and a plugin reference, but it does not cite CISA KEV listing or confirmed active exploitation. Treat exploitation as plausible against outdated clients, not proven in the provided evidence.

Researcher notes

Core evidence identifies PuTTY before 0.75 on Windows and an availability-only GUI hang. The record does not provide affected CPEs, CWE classification, or confirmed exploitation. Be careful not to generalize Linux impact beyond the source note about similar GUI behavior.

Mitigation direction

  • Upgrade Windows PuTTY clients to version 0.75 or later.
  • Inventory admin workstations and jump hosts for outdated PuTTY installations.
  • Prefer trusted SSH endpoints until affected clients are upgraded.
  • Check PuTTY vendor guidance for any platform-specific notes.

Validation and detection

  • Confirm installed PuTTY versions on Windows systems are 0.75 or later.
  • Review software inventory for portable or unmanaged PuTTY copies.
  • Check whether administrators connect to untrusted or third-party SSH servers.
  • Document any Linux or other GUI exposure separately, because evidence is less specific.
Prepared
Confidence
high
Sources
5

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.

ATT&CK lookup starting points

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CVE-2021-33500 mapping review

Open the CVE-to-ATT&CK bridge for reviewed, inferred, or future official mappings tied to this CVE.

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Vulnerability profileCVE Program record
Severity
High
CVSS
7.5 (3.1)
Known Exploited
No
Published

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

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.

1CVSS vectors
0Timeline events
0ADP providers
4Source links

CVSS vector scores

1 official score

We collect every scored CVSS vector available in the official CNA and ADP containers. When more than one version is present, the table keeps the source vectors side by side instead of collapsing them into the highest score.

ScoreVersionSeverityVectorExploitImpactSource
7.5CVSS 3.1HighCVSS:3.1/AC:L/AV:N/A:H/C:N/I:N/PR:N/S:U/UI:N3.93.6Primary CVE score

Vulnerability scoring details

Base CVSS 3.1 score

7.5High
CVSS 3.1 vector shape for CVE-2021-33500Attack VectorAttack ComplexityPrivileges RequiredUser InteractionScopeConfidentiality ImpactIntegrity ImpactAvailability Impact

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

Attack Vector
NetworkAdjacentLocalPhysical
Attack Complexity
LowHigh
Privileges Required
NoneLowHigh
User Interaction
NoneRequired
Scope
ChangedUnchanged
Confidentiality Impact
HighLowNone
Integrity Impact
HighLowNone
Availability Impact
HighLowNone

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.