CVE-2021-27135

CRITICALNVD 9.89.8—
EchelonGraph scoreMEDIUM confidence

Score 9.8 from GitHub Security Advisory (severity: CRITICAL) published 2022-05-24. NVD baseline CVSS 9.8; sources differ by 0.0.

Triggered by: GitHub Security Advisory CVSS
Sources: epss, ghsa, nvd
9.8EG
EchelonGraph verdictPlan a fixSerious severity, but no confirmed exploitation yet.
  • High severity, but no confirmed exploitation yet
CISA-KEV: Not listedEPSS PROB: 8%CVSS: 9.8Exploit: None knownExposed: 0

A fix is available — apply it.

xterm before Patch #366 allows remote attackers to execute arbitrary code or cause a denial of service (segmentation fault) via a crafted UTF-8 combining character sequence.

CVSS v3
9.8
EG Score
9.8(medium)
EG Risk
52(Track)
EG Risk 52/100SSVC: Track

EG Risk is EchelonGraph's 0–100 priority score: it fuses intrinsic severity with real-world exploitation and automatability so you can rank equal-severity CVEs and fix the most dangerous first. Higher = act sooner. Distinct from the 0–10 EG Score (severity).

How it’s computed
Severity98% × 45%
Exploitation8% × 40%
Automatability30% × 15%
Action: Routine — remediate on your standard cadence.
EPSS PROB
8%
EPSS %ILE
94%
KEV
Not listed

Published

February 10, 2021

Last Modified

November 21, 2024

Advisory Details (10)

Auto-updated Aug 15, 2026
Patch available. Sources: github_commit, redhat.
generic Patch Available

CVE-2021-27135: xterm flaw may allow remote code execution, CVSS 9.6 | Hacker News

https://news.ycombinator.com/item?id=26524650
generic

[SECURITY] Fedora 33 Update: xterm-366-1.fc33 - package-announce - Fedora mailing-lists

https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/35LK2ZXEIJUOGOA7FV2TJL3L6LFJ4X5S/
generic Patch Available

[SECURITY] [DLA 2558-1] xterm security update

https://lists.debian.org/debian-lts-announce/2021/02/msg00019.html
generic
https://invisible-island.net/xterm/xterm.log.html
github_commit

commit 82ba55b8f994 (ThomasDickey/xterm-snapshots)

Fix landed in ThomasDickey/xterm-snapshots commit 82ba55b8f994 — awaiting tagged release

https://github.com/ThomasDickey/xterm-snapshots/commit/82ba55b8f994ab30ff561a347b82ea340ba7075c
generic

Making sure you're not a bot!

https://bugzilla.suse.com/show_bug.cgi?id=1182091
redhat Patch Available

1927559 – (CVE-2021-27135) CVE-2021-27135 xterm: crash when processing combining characters

Affected: Red Hat Enterprise Linux 8

https://bugzilla.redhat.com/show_bug.cgi?id=1927559
redhat Patch Available

CVE-2021-27135 - Red Hat Customer Portal

Affected: Red Hat Enterprise Linux 8 or OpenShift Container Platform 4, is affected by this vulnerability and a fix may be released to a

https://access.redhat.com/security/cve/CVE-2021-27135
generic

oss-security - Re: Re: screen crash processing combining characters

http://www.openwall.com/lists/oss-security/2021/02/10/7
generic

Full Disclosure: CVE-2021-31535 libX11 Insufficient Length Checks PoC and Archeology

http://seclists.org/fulldisclosure/2021/May/52

Patch Availability(5)

Vendor / EcosystemFixed in / PatchReleasedSource
ubuntuxterm (322-1ubuntu1.2) @ xenial2026-05-26ubuntu
redhatxterm-0:331-1.el8_1.12021-02-24redhat
redhatxterm-0:331-1.el8_2.12021-02-24redhat
redhatxterm-0:295-3.el7_9.12021-02-22redhat
redhatxterm-0:331-1.el8_3.22021-02-18redhat

Patches are aggregated from vendor advisories (Red Hat, Microsoft, Cisco, GitHub) and package ecosystems (OSV, GHSA). Multiple rows for the same upstream release have been deduplicated.

Affected Packages

(5 across 5 ecosystems)
Debian:11(1)
PackageVulnerable rangeFixed inDependents
xterm—366-1—
Debian:12(1)
PackageVulnerable rangeFixed inDependents
xterm—366-1—
Debian:13(1)
PackageVulnerable rangeFixed inDependents
xterm—366-1—
Debian:14(1)
PackageVulnerable rangeFixed inDependents
xterm—366-1—
Debian:9(1)
PackageVulnerable rangeFixed inDependents
xterm327-2327-2+deb9u1—

All Vendor Advisories

(6)

Every vendor that published an advisory referencing this CVE — pulled from our cve_vendor_advisories aggregation. Click any row for the vendor's original advisory page.

Data Freshness Timeline

(refreshed 9× in last 7d / 33× in last 30d)

Each row is a source pipeline that fetched or updated this CVE on that date, with what changed. For example, "NVD update" means NVD published or revised its analysis for this CVE; "MITRE cvelistV5" means we ingested or refreshed it from the CNA feed. Most recent first.

Showing the most recent 100 of 132 total refreshes for this CVE.

  1. 2026-08-20 22:52 UTCEPSS rescore
  2. 2026-08-20 09:01 UTCOSV refresh
  3. 2026-08-19 17:01 UTCEPSS rescore
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  7. 2026-07-23 01:59 UTCEG score recompute
  8. 2026-07-22 22:45 UTCEG score recompute
  9. 2026-07-22 14:06 UTCEPSS rescore
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  43. 2026-07-01 09:18 UTCOSV refresh
  44. 2026-06-30 23:20 UTCEPSS rescore
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  72. 2026-06-13 14:43 UTCOSV refresh
  73. 2026-06-12 23:10 UTCEPSS rescore
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Frequently asked(5)

What is CVE-2021-27135?
CVE-2021-27135 is a critical vulnerability published on February 10, 2021. xterm before Patch #366 allows remote attackers to execute arbitrary code or cause a denial of service (segmentation fault) via a crafted UTF-8 combining character sequence.
When was CVE-2021-27135 disclosed?
CVE-2021-27135 was first published in the National Vulnerability Database on February 10, 2021, with the most recent update on November 21, 2024. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
Is CVE-2021-27135 actively exploited?
CVE-2021-27135 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 8% probability of exploitation in the next 30 days, which ranks it in the top 6.0% of all scored CVEs.
What is the CVSS score of CVE-2021-27135?
CVE-2021-27135 has a CVSS v3 base score of 9.8 (NVD).
How do I remediate CVE-2021-27135?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2021-27135, EchelonGraph cross-links them in the Vendor Advisories panel below — those typically contain the canonical remediation steps, fixed version numbers, and any vendor-specific mitigations.

Dependency Blast Radius

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