BlackTreeCVE Intelligence
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Full vulnerability report · 2021
CVE-2021-26937High confidence

n/a — Improper Neutralization of Argument Delimiters in a Command ('Argument Injection')

Unknown · Unknown

9.8CriticalCVSS 3.1
Recommended action
Within 72 hours

Critical technical impact with a remotely reachable, unauthenticated path and a public exploit reference; no CISA KEV confirmation is currently recorded.

Fix not verified
R
Operational reassessment

Published severity in operational context

Open reassessment dashboard →
Published severityCriticalOperational priority:Critical, unchanged from published severity.unchanged

Evidence used

  • No CISA KEV confirmation is currently recorded.
  • A structured source references public exploit or proof-of-concept material.
  • The selected CVSS metric records a network-reachable, unauthenticated path with no user interaction.
  • EPSS is 9.15% for the current model date.

Compensating controls

  • Restrict the affected network interface to trusted sources where business-safe.
  • Increase monitoring for the attack path and post-exploitation behaviour described in the report.

Verification

  1. Confirm that the asset runs Unknown Unknown and falls inside the recorded affected range.
  2. Recheck the vendor advisory before scheduling a change because no verified fixed version is currently retained.
  3. Validate exposure, authentication requirements and compensating controls in the actual environment.
  4. Reopen this reassessment when CVSS, KEV, EPSS, exploit evidence or remediation changes.
Mitigation target: Within 3 daysRemediation target: Within 90 days

This automated reassessment organises public evidence. It does not know asset exposure, business impact or control effectiveness and does not replace CVSS or a human risk decision.

Distribution package intelligence

Release-specific package status

Alpine, Debian findings are scoped to the named distribution, release and source package. An absent finding does not mean a package is unaffected.

7 package states
Repository candidate not checked

A published vendor fix does not prove that a matching update is enabled and installable on a particular asset. Confirm the local package candidate before scheduling remediation.

Distribution releaseSource packageVendor stateFixed versionEvidence
Alpine v3.23v3.23 · mainscreenVendor fix publishedAlpine records a security fix at this version. An absent entry does not mean the package is unaffected.4.8.0-r4Alpine Security Database ↗Source updated 3 Oct 2026
Alpine v3.22v3.22 · mainscreenVendor fix publishedAlpine records a security fix at this version. An absent entry does not mean the package is unaffected.4.8.0-r4Alpine Security Database ↗Source updated 3 Oct 2026
Alpine v3.21v3.21 · mainscreenVendor fix publishedAlpine records a security fix at this version. An absent entry does not mean the package is unaffected.4.8.0-r4Alpine Security Database ↗Source updated 3 Oct 2026
Debian trixietrixie · sourcescreenVendor fix publishedDebian records a fixed source-package version for this release.4.8.0-5Debian Security Tracker ↗Source updated 5 Oct 2026
Debian bookwormbookworm · sourcescreenVendor fix publishedDebian records a fixed source-package version for this release.4.8.0-5Debian Security Tracker ↗Source updated 5 Oct 2026
Debian forkyforky · sourcescreenVendor fix publishedDebian records a fixed source-package version for this release.4.8.0-5Debian Security Tracker ↗Source updated 5 Oct 2026
Debian sidsid · sourcescreenVendor fix publishedDebian records a fixed source-package version for this release.4.8.0-5Debian Security Tracker ↗Source updated 5 Oct 2026
Optional official sources

National CERT insights
?CERT means Computer Emergency Response Team; CSIRT is the closely related term Computer Security Incident Response Team.

Choose official national sources for this report. Each advisory shows its original language. Your selection is remembered on this device and included in shared links.

Official European source

ENISA European Vulnerability Database

Official EUVD identifiers, advisory evidence and known-exploited context. Missing fields are not treated as evidence of low risk.

1 current
ENISA EUVD identifier

EUVD-2021-13719

No EUVD known-exploited evidence

ENISA has published the identifier mapping but no EUVD description has been stored yet.

EUVD state
Present in the current official mapping
Known exploitation
Not present in the current ENISA EUVD known-exploited dataset. This is not proof of no exploitation.
ENISA score
Not supplied in the stored EUVD record
Advisory evidence
No linked advisory details stored yet
Recommended actionWithin 72 hours

Critical technical impact with a remotely reachable, unauthenticated path and a public exploit reference; no CISA KEV confirmation is currently recorded.

Fix not verified
01

What, why and how

encoding.c in GNU Screen through 4.8.0 allows remote attackers to cause a denial of service (invalid write access and application crash) or possibly have unspecified other impact via a crafted UTF-8 character sequence.

What

encoding.c in GNU Screen through 4.8.0 allows remote attackers to cause a denial of service (invalid write access and application crash) or possibly have unspecified other impact via a crafted UTF-8 character sequence.

Why

The product constructs a string for a command to be executed by a separate component in another control sphere, but it does not properly delimit the intended arguments, options, or switches within that command string.

How

An attacker operating through a network path may attempt exploitation without authentication or user interaction. If successful, the issue may disrupt the affected service.

What

encoding.c in GNU Screen through 4.8.0 allows remote attackers to cause a denial of service (invalid write access and application crash) or possibly have unspecified other impact via a crafted UTF-8 character sequence.

Why

The product constructs a string for a command to be executed by a separate component in another control sphere, but it does not properly delimit the intended arguments, options, or switches within that command string.

How

An attacker operating through a network path may attempt exploitation without authentication or user interaction. If successful, the issue may disrupt the affected service.

02

Exploit reality and attack path

CVSS severity, EPSS forecast probability, public exploit material and CISA-confirmed exploitation are separate signals.

Observed exploitation
?Confirmed exploitation and public exploit material are separate signals. Attacks can occur without public proof-of-concept or exploit code.
No confirmed evidence

No CISA KEV match was present at the last successful refresh. This means no confirmation from that source, not proof of no exploitation.

Public PoC / exploit material
?Confirmed exploitation and public exploit material are separate signals. Attacks can occur without public proof-of-concept or exploit code.
Reference recorded

A structured CVE source labels at least one public reference as exploit material. BlackTree has not independently validated that it is safe, reliable or weaponised.

Likely attack path
a network path → Improper Neutralization of Argument Delimiters in a Command ('Argument Injection') → disrupt the affected service
Attack surface
Network
Privileges required
None: unauthenticated exploitation is possible
User interaction
None
Attack complexity
Low: no specialised conditions are recorded
Security boundary
Unchanged: impact remains within the vulnerable component's security authority
Weakness
?CWE means Common Weakness Enumeration: a standard category for the underlying weakness.
CWE-88 ↗

CWE-88: Improper Neutralization of Argument Delimiters in a Command ('Argument Injection'). The product constructs a string for a command to be executed by a separate component in another control sphere, but it does not properly delimit the intended arguments, options, or switches within that command string.

CVSS vector
?CVSS means Common Vulnerability Scoring System. The vector records the metric values used to calculate technical severity.
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Common Vulnerability Scoring System 3.1: the compact vector below is decoded into plain language.

AVNetworkAttack vector: The vulnerable component can be reached over a network.ACLowAttack complexity: No specialised conditions are required beyond attacker-controlled input.PRNonePrivileges required: The attacker does not need an account or existing privileges.UINoneUser interaction: No action by another user is required.SUnchangedScope: The security impact remains within the vulnerable component's authority.CHighConfidentiality impact: A successful attack can cause a major loss.IHighIntegrity impact: A successful attack can cause a major loss.AHighAvailability impact: A successful attack can cause a major loss.
Post-exploitation / living off the land
No specific living-off-the-land technique is confirmed in the structured sources. Monitor normal administration tools for activity inconsistent with the affected service's baseline.
NetworkUnauthenticatedDenial of serviceCWE-88Public exploit reference
A

Official authority intelligence

Only matched European and national findings are included. Language selectors and unavailable sources are omitted.

Cyber Security Agency of Singapore · English · CSA-SB-20210210Security Bulletin 10 Feb 2021

The Cyber Security Agency of Singapore included this CVE in its official Security Bulletin 10 Feb 2021, published on 10 February 2021. Open the linked bulletin for the product, severity and reference information published in that issue.

Official advisory ↗
CERT-FR · French · CERTFR-2021-AVI-638Multiples vulnérabilités dans Juniper Junos Space

ecord?id=CVE-2020-28374 Référence CVE CVE-2020-29573 https://www.cve.org/CVERecord?id=CVE-2020-29573 Référence CVE CVE-2020-29661 https://www.cve.org/CVERecord?id=CVE-2020-29661 Référence CVE CVE-2020-7053 https://www.cve.org/CVERecord?id=CVE-2020-7053 Référence CVE CVE-2021-20265 https://www.cve.org/CVERecord?id=CVE-2021-20265 Référence CVE CVE-2021-20277 https://www.cve.org/CVERecord?id=CVE-2021-20277 Référence CVE CVE-2021-20305 https://www.cve.org/CVERecord?id=CVE-2021-20305 Référence CVE CVE-2021-2163 https://www.cve.org/CVERecord?id=CVE-2021-2163 Référence CVE CVE-2021-25215 https://www.cve.org/CVERecord?id=CVE-2021-25215 Référence CVE CVE-2021-26937 https://www.cve.org/CVERecord?id=CVE-2021-26937 Référence CVE CVE-2021-27363 https://www.cve.org/CVERecord?id=CVE-2021-27363 Référence CVE CVE-2021-27364 https://www.cve.org/CVERecord?id=CVE-2021-27364 Référence CVE CVE-2021-27365 https://www.cve.org/CVERecord?id=CVE-2021-27365 Référence CVE CVE-2021-27803 https://www.cve.org/CVERecord?id=CVE-2021-27803 Gestion détaillée du document le 18 août 2021 Version initiale Alertes Avis Bulletins d’actualités Mentions légales Conditions générales À propos Contact cyber.gouv.fr service-public.fr legifrance.gouv.fr info.gouv.fr france.fr info.gouv.fr/risques Premier Ministre / Secrétariat Général de la

Official advisory ↗
JVN iPedia · Japanese · JVNDB-2021-003775GNU Screen における引数の挿入または変更に関する脆弱性

GNU Screen には、引数の挿入または変更に関する脆弱性が存在します。

Official advisory ↗
03

Patch and workaround

Operational remediation based on structured source evidence.

Status
?Patch availability is based on structured fixed-version fields and authoritative update references. If no fix is verified, check the vendor advisory before making a change.
Fix not verified
Affected
n/a
Fixed
No fixed version is explicitly recorded in the structured CVE data.
Action
No verified patch reference is present in the current structured sources. Check the vendor advisory before making a change.
Workaround
No verified workaround is recorded. If business-safe, reduce exposure to the affected interface and allow only trusted sources until authoritative guidance is available.
04

Evidence and provenance

Published 9 Feb 2021 · Last source change 9 May 2025, 20:03 UTC · CWE-88 · Improper Neutralization of Argument Delimiters in a Command ('Argument Injection')

CVE recordCVE.org · 5.1
CVSS sourceNIST NVD
EPSS source
?The date BlackTree first stored a score for this CVE from the daily FIRST EPSS feed.
FIRST · tracked since 2026-08-14
European sourceENISA EUVD · EUVD-2021-13719
Product sourceUnavailable
Remediation sourceCVE/CNA references
CWE sourceNIST NVD
NVD statusNVD modified after enrichment

Missing structured fields: affected product. Missing data is not evidence of low risk; review the primary advisory.

Material change intelligence

What changed after publication

View recent updates ↗

No material field changes have been recorded since change tracking began. Routine source refreshes and cosmetic edits are intentionally excluded.

Material fields only · duplicate refreshes suppressed · history retained for the configured operational retention period
CVE published
ENISA EUVD · EUVD-2021-13719↗Public exploit reference↗Public exploit reference↗Official CVE record (CNA and ADP data)↗NVD record↗
Technical terms and abbreviations used in this report
CVE
Common Vulnerabilities and Exposures: the public identifier for one disclosed vulnerability.
CVSS
Common Vulnerability Scoring System: a technical severity framework; it is not patching priority by itself.
EPSS
Exploit Prediction Scoring System: FIRST's estimate of the probability that exploitation activity will be observed in the next 30 days; it is a forecast, not confirmation.
CWE
Common Weakness Enumeration: the standard category describing the underlying software or hardware weakness.
CNA
CVE Numbering Authority: an organisation authorised to assign and publish CVE records.
CISA ADP
Cybersecurity and Infrastructure Security Agency Authorized Data Publisher: structured enrichment added to a CVE record.
NVD
National Vulnerability Database: NIST's enrichment service for CVE records.
CERT / CSIRT
A computer security incident response team that publishes warnings or coordinates incident response.
PoC
Proof of concept: public material that demonstrates or helps reproduce exploitation.
CSAF
Common Security Advisory Framework: a machine-readable format for security advisories.
LoTL
Living off the land: abuse of legitimate tools or system functions during an attack.
Free version - for non-commercial use only.CVE-2021-26937 · cve.blacktree.nl