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CVE Record

CVE-2020-27783: A XSS vulnerability was discovered in python-lxml's clean module.

A XSS vulnerability was discovered in python-lxml's clean module. The module's parser didn't properly imitate browsers, which caused different behaviors between the sanitizer and the user's page. A remote attacker could exploit this flaw to run arbitrary HTML/JS code.

MediumCVSS 6.1Not KEV-listedUpdated
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Glexia's TakeAutomated analysismoderate

Security readout for executives and security teams

Plain-English summary

CVE-2020-27783 is a cross-site scripting issue in python-lxml's clean module. If an application used this sanitizer on untrusted HTML and then rendered the result in a browser, an attacker could get script or HTML through because lxml did not match browser parsing behavior.

Executive priority

Treat as a moderate-priority web application dependency issue. Prioritize internet-facing applications that process user-submitted HTML, customer content, comments, tickets, or rich text. Patch through normal dependency and vendor update channels, with validation focused on actual sanitizer usage.

Technical view

The flaw is CWE-79 in python-lxml lxml-4.6.2. The clean module parser handled input differently from browsers, creating sanitizer bypass conditions. The CVSS 3.1 score is 6.1, network exploitable with low complexity, no privileges, and required user interaction, with changed scope and low confidentiality/integrity impact.

Likely exposure

Exposure is most likely in Python applications or products that include python-lxml and use its clean module to sanitize attacker-controlled HTML before browser display. Systems merely having lxml installed but not using this sanitizer path have less direct exposure.

Exploitation context

The source bundle does not show CISA KEV listing or confirmed active exploitation. Exploitation would require a target application that accepts hostile HTML, sanitizes it with affected lxml behavior, and renders the output to a user who interacts with the affected page.

Researcher notes

Evidence identifies python-lxml lxml-4.6.2 and the clean module parser mismatch as the affected condition. The bundle lists multiple vendor advisories but does not provide exploit proof, KEV status, or a complete fixed-version matrix, so remediation should follow the relevant platform advisory.

Mitigation direction

  • Inventory python-lxml/lxml usage, especially lxml-4.6.2 and downstream packaged builds.
  • Apply relevant Debian, Fedora, Oracle, NetApp, or vendor-provided lxml security updates.
  • Review code paths using the lxml clean module on untrusted HTML.
  • Check vendor guidance before substituting sanitizer behavior or changing browser-rendered content handling.

Validation and detection

  • Confirm deployed package versions against the applicable vendor advisory or package changelog.
  • Search application code for lxml clean module imports and sanitizer wrappers.
  • Verify whether sanitized untrusted HTML is later rendered in browser-facing pages.
  • Add regression tests for sanitizer expectations without including weaponized payloads.
Prepared
Confidence
high
Sources
9

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

Use these exact CWE pages and searches to review the Glexia ATT&CK library from this CVE's weakness and description context.

cwe · medium confidence lookup

CWE-79: User-session and phishing behavior lookup

Client-side and session-facing weaknesses should be reviewed alongside initial-access and user-execution behaviors. Open the exact CWE lookup page first, then review the ATT&CK searches from that MITRE weakness context. This is a Glexia lookup hint, not an official ATT&CK mapping.

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cve · low confidence lookup

CVE-2020-27783 mapping review

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Vulnerability profileCVE Program record
Severity
Medium
CVSS
6.1 (3.1)
Known Exploited
No
Published

Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A: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
9Source 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
6.1CVSS 3.1MediumCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N2.82.7Primary CVE score

Vulnerability scoring details

Base CVSS 3.1 score

6.1Medium
CVSS 3.1 vector shape for CVE-2020-27783Attack VectorAttack ComplexityPrivileges RequiredUser InteractionScopeConfidentiality ImpactIntegrity ImpactAvailability Impact

Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A: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/apython-lxmllxml-4.6.2Listed
Weakness

CWE details

CWE-79

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