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CVE-2021-26937

34
FAUCET Score

CVE-2021-26937 is a critical denial-of-service vulnerability affecting GNU Screen versions up to 4.8.0, as well as various Debian and Fedora distributions. An unauthenticated remote attacker can exploit this flaw by sending a specially crafted UTF-8 character sequence, leading to an application crash and potentially other unspecified impacts. With a CVSS score of 9.8, this vulnerability is easily exploitable over the network with low attack complexity, posing a high risk to confidentiality, integrity, and availability. While no public exploit code or active exploitation has been observed, and community discussion is minimal, its high EPSS score suggests a non-negligible probability of future exploitation.

Impacted Technologies

VendorProductVersion(s)CPE
<= 4.8.0CPE matchmatch criteria
cpe:2.3:a:gnu:screen:*:*:*:*:*:*:*:*
9.0CPE matchmatch criteria
cpe:2.3:o:debian:debian_linux:9.0:*:*:*:*:*:*:*
10.0CPE matchmatch criteria
cpe:2.3:o:debian:debian_linux:10.0:*:*:*:*:*:*:*
32CPE matchmatch criteria
cpe:2.3:o:fedoraproject:fedora:32:*:*:*:*:*:*:*
33CPE matchmatch criteria
cpe:2.3:o:fedoraproject:fedora:33:*:*:*:*:*:*:*

CVSS Data

CVSS version used by this source: 3.1

9.8CRITICAL

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

Attack Vector
NETWORK
Attack Complexity
LOW
Privileges Required
NONE
User Interaction
NONE
Scope
UNCHANGED
Confidentiality Impact
HIGH
Integrity Impact
HIGH
Availability Impact
HIGH
Exploitability Score
3.9
Impact Score
5.9
CvssVersion
3.1

Exploit Intelligence

EPSS Score
9.15%
Probability of exploitation in next 30 days
EPSS Percentile
94.8%
Percentile rank of EPSS score among Peer Group
As of 2026-07-27
Model: v2026.06.15
This CVE's current EPSS score of 0.0915 is in the 90th percentile among its peer group of 36,862 CVEs.

Social Chatter

The average CVE in this peer group has 0.0 Twitter, 0.1 Reddit, 0.3 Bluesky, 0.3 Mastodon, and 2.4 GitHub mentions.

Media Mentions

No media coverage found for this CVE.

The average CVE in this peer group has 0.3 InfoSec Media, 0.0 Vendor Blog, and 0.0 Security Researcher mentions.

Remediation

Patch Available

Vendor Patches (6)

microsoftpatch availablevia msrc
Product: 18382-16823Fixed in: 4.9.1-1
microsoftpatch availablevia msrc
Product: cbl2 screen 4.9.1-1 on CBL Mariner 2.0Fixed in: 4.9.1-1
redhatpatch availablevia redhat_api
Product: Red Hat Enterprise Linux 7Fixed in: screen-0:4.1.0-0.27.20120314git3c2946.el7_9
View patch
redhatpatch availablevia redhat_api
Product: Red Hat Enterprise Linux 7.7 Advanced Update SupportFixed in: screen-0:4.1.0-0.25.20120314git3c2946.el7_7.1
View patch
redhatpatch availablevia redhat_api
Product: Red Hat Enterprise Linux 7.7 Telco Extended Update SupportFixed in: screen-0:4.1.0-0.25.20120314git3c2946.el7_7.1
View patch
redhatpatch availablevia redhat_api
Product: Red Hat Enterprise Linux 7.7 Update Services for SAP SolutionsFixed in: screen-0:4.1.0-0.25.20120314git3c2946.el7_7.1
View patch

Vendor Advisories (2)

redhatCVE-2021-26937Important

screen: crash when processing combining chars

Feb 10, 2021
microsoft2021-Feb/CVE-2021-26937Critical

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.

Feb 9, 2021

References

security.netapp.com / advisory/ntap-20250509-0004
ftp.gnu.org / gnu/screen
Product
lists.debian.org / debian-lts-announce/2021/02/msg00031.html
Mailing ListThird Party Advisory
lists.fedoraproject.org / archives/list/package-announce%40lists.fedoraproject.org/message/GNWBOIDEPOEQS5RMQVMFKHKXJCGNYWBL
lists.fedoraproject.org / archives/list/package-announce%40lists.fedoraproject.org/message/JJWLXP45POUUYBJRRWPVAWNZDJTLYWVM
lists.gnu.org / archive/html/screen-devel/2021-02/msg00000.html
ExploitMailing ListVendor Advisory
security.gentoo.org / glsa/202105-11
Third Party Advisory
debian.org / security/2021/dsa-4861
Third Party Advisory
openwall.com / lists/oss-security/2021/02/09/3
ExploitMailing ListThird Party Advisory
openwall.com / lists/oss-security/2021/02/09/8
ExploitMailing ListThird Party Advisory