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NVD / CVE Program· CNA mitre

CVE-2021-26937: 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

Noroxi assessment

Priority: Plan (action score 42/100)

  • The sources we track (CISA KEV, Exploit-DB, Metasploit, Nuclei, GitHub) show no public exploit code or exploitation in the wild.
  • Probability of exploitation in the next 30 days: 9.1% (FIRST EPSS); higher than 95.3% of all records.
  • Anyone who can reach it over the internet can trigger it. No account or password is required. No user action is required. No special conditions are required; it is repeatable.
  • Fixed version: screen (Alpine:v3.10) 4.6.2-r2; screen (Alpine:v3.11) 4.7.0-r2; screen (Alpine:v3.12) 4.8.0-r1.

Add it to your regular patch cycle. Upgrade to screen (Alpine:v3.10) 4.6.2-r2; screen (Alpine:v3.11) 4.7.0-r2; screen (Alpine:v3.12) 4.8.0-r1 or later.

Generated automatically from the record's data: CVSS (NVD and CNA), CISA KEV and SSVC, FIRST EPSS, exploit sources, fixed versions. How we calculate it

Primary sources: NVD · CVE.org · FIRST EPSS

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.

CriticalCVSS 9.8 · v3.1—No exploit Fix available
Published
Feb 9, 2021
Updated
Jun 16, 2026
EPSS
9.1% · 95th percentile

Report tools

JSON

Action score

42

Plan

Add it to your regular patch cycle.

CVSS
39 / 40 · 9.8 / 10
CISA KEV
0 / 30 · Not listed
EPSS
3 / 30 · 9.1%

Get told when this record changes

  • Not in KEV: no record of exploitation in the wild
  • No public exploit code on record
  • A fix has been released

If any of these changes, we'll tell you in the daily email digest.

Follow CVE-2021-26937

When you'll hear from us

  • when it enters CISA KEV
  • when exploit code appears or is weaponized
  • when the record is updated (including a fixed version)
  • when EPSS rises 20 points in a week

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Noroxi analysis

What does it mean in your environment?

The assessment above is generated automatically from the record's data; it doesn't know your environment. Our team verifies on your systems whether this vulnerability is actually exploitable and which mitigation is enough.

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Affected systems

Is your version affected?

Pick the product and type the version you run. It's compared with this record's version ranges in your browser; the version isn't sent anywhere.

VendorProduct
gnuscreen
debiandebian linux
fedoraprojectfedora

Affected versions

NVD version ranges (for catalog products). Add the product to your stack with a version and matching uses these.

  • debian debian linux10.0
  • debian debian linux9.0
  • fedoraproject fedora32
  • fedoraproject fedora33
  • gnu screenup to 4.8.0 inclusive

Package-level exposure

OSV and GitHub Advisory data: ecosystem, package and range. SBOM matching uses this table.

EcosystemPackageAffected rangeFix
Alpine:v3.10screenbefore 4.6.2-r24.6.2-r2
Alpine:v3.11screenbefore 4.7.0-r24.7.0-r2
Alpine:v3.12screenbefore 4.8.0-r14.8.0-r1
Alpine:v3.13screenbefore 4.8.0-r44.8.0-r4
Debian:10screenbefore 4.6.2-3+deb10u14.6.2-3+deb10u1
Debian:12screenbefore 4.8.0-54.8.0-5
Debian:9screenbefore 4.5.0-6+deb9u14.5.0-6+deb9u1
openSUSE:Leap 15.2screenbefore 4.6.2-lp152.6.3.14.6.2-lp152.6.3.1
openSUSE:Tumbleweedscreenbefore 4.9.0-1.14.9.0-1.1
Red Hat:enterprise_linux:7::clientscreenbefore 0:4.1.0-0.27.20120314git3c2946.el7_90:4.1.0-0.27.20120314git3c2946.el7_9
Red Hat:enterprise_linux:7::clientscreen-debuginfobefore 0:4.1.0-0.27.20120314git3c2946.el7_90:4.1.0-0.27.20120314git3c2946.el7_9
Red Hat:rhel_aus:7.7::serverscreenbefore 0:4.1.0-0.25.20120314git3c2946.el7_7.10:4.1.0-0.25.20120314git3c2946.el7_7.1
Red Hat:rhel_aus:7.7::serverscreen-debuginfobefore 0:4.1.0-0.25.20120314git3c2946.el7_7.10:4.1.0-0.25.20120314git3c2946.el7_7.1
SUSE:HPE Helion OpenStack 8screenbefore 4.0.4-23.6.14.0.4-23.6.1
SUSE:Linux Enterprise Module for Basesystem 15 SP2screenbefore 4.6.2-5.3.14.6.2-5.3.1

Same product

gnu: all records

Other highest-scoring records for the same primary product.

  • CVE-2003-0972Integer signedness error in ansi.c for GNU screen 4.0.1 and earlier, and 3.9.15 and earlier, allows local users to execute arbitrary code vi
    41Plan
  • CVE-2020-9366A buffer overflow was found in the way GNU Screen before 4.8.0 treated the special escape OSC 49.
    40Plan
  • CVE-2017-5618GNU screen before 4.5.1 allows local users to modify arbitrary files and consequently gain root privileges by leveraging improper checking o
    31Monitor

Published before and after this one in the same product

  • ← EarlierCVE-2007-3048Jun 5, 2007 · GNU screen 4.0.3 allows local users to unlock the screen via a CTRL-C sequence at the password prompt.
    28Monitor
  • ← EarlierCVE-2009-1214Apr 1, 2009 · GNU screen 4.0.3 creates the /tmp/screen-exchange temporary file with world-readable permissions, which might allow local users to obtain se
    19Monitor
  • Later →CVE-2023-24626Apr 8, 2023 · socket.c in GNU Screen through 4.9.0, when installed setuid or setgid (the default on platforms such as Arch Linux and FreeBSD), allows loca
    26Monitor

Remediation

Which version to upgrade to

Fix versions compiled from the vendor, package registries and Microsoft. Verify the vendor's note before upgrading.

Product / packageFixed versionSource
alpine:screen4.6.2-r2 · Alpine:v3.10Package registry (OSV)
debian:screen4.8.0-5 · Debian:12Package registry (OSV)
opensuse:screen4.6.2-lp152.6.3.1 · openSUSE:Leap 15.2Package registry (OSV)
red hat:screen0:4.1.0-0.27.20120314git3c2946.el7_9 · Red Hat:enterprise_linux:7::clientPackage registry (OSV)
red hat:screen-debuginfo0:4.1.0-0.27.20120314git3c2946.el7_9 · Red Hat:enterprise_linux:7::clientPackage registry (OSV)
suse:screen4.0.4-23.6.1 · SUSE:HPE Helion OpenStack 8Package registry (OSV)

Exploit status

No known public exploit

No public exploit has been observed yet. That doesn't mean you're safe, only that the bar is a little higher.

Research context

For pentesters and researchers: attack profile, score disagreement, timeline, patch commits, credits, variant and chain candidates, bug bounty scope. All derived from existing data; no exploit code.

Timeline

From publication to today: proof of concept, Metasploit module, CISA KEV and fix record. Dates are as reported by the sources.

No dated events beyond publication.

No history yet (it accumulates with the daily EPSS job).

Patch and commit links

Commit, PR and diff links among the references. A starting point for patch-diffing and variant hunting; fixes, not exploits.

No commit or PR link among the references.

Credits

All researchers

Finders, reporters and analysts named in the CNA record. Click a name for that researcher’s other records.

No credits in the CNA record.

Variant candidates

Same product, same weakness class, within 18 months. If the patch missed the root cause, the sibling bug is here.

No nightly-computed relations.

Chain candidates

An authentication bypass and a privilege-requiring bug in the same product, published close together: combined they may become an unauthenticated path.

—

Bug bounty scope

No known public program.

Source: bounty-targets-data (public HackerOne, Bugcrowd, Intigriti, YesWeHack listings).

Technical details

Attack conditions

  • Anyone who can reach it over the internet can trigger it.
  • No account or password is required.
  • No user action is required.
  • No special conditions are required; it is repeatable.

If successful

Confidentiality
high · data can be read
Integrity
high · data or configuration can be modified
Availability
high · the service can be disrupted
Attack vector
Network
Attack complexity
Low
Privileges required
None
User interaction
None
Scope
Unchanged
Confidentiality impact
High
Integrity impact
High
Availability impact
High

Weakness class (CWE)

CWE-88 · Improper Neutralization of Argument Delimiters in a Command ('Argument Injection')

CVSS vector

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

nvd-primary

Attack context

MITRE CAPEC attack patterns and ATT&CK techniques for this weakness class (CWE). A starting point for detection rules and threat hunting.

ATT&CK techniques

—

Change log

  1. Fix✗ → ✓

For records you follow, these changes also arrive as notifications. →

References

Show all references (6 more)

Vendor advisories and official records. Exploit/PoC links are deliberately left out.

All records