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: 7.8%CVSS: 9.8Exploit: None knownExposed services: Not assessed

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
9.8CRITICALmedium confidence
EG Risk
52
EG Risk 52/100CISA SSVC

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%
CISA SSVC: Track at low or medium mission impact; Track* or Attend at high (mission-essential systems).
Action: A fix is available. Apply it within your standard update timelines at low or medium mission impact and sooner than that at high.
EPSS PROB
7.8%
EPSS %ILE
94th
KEV
Not listed

CISA SSVCTrack at low or medium mission impact; Track* or Attend at high (mission-essential systems).

A fix is available. Apply it within your standard update timelines at low or medium mission impact and sooner than that at high.

Exploitation none (no KEV listing, exploit record or EPSS ≥ 50%) · Automatable unknown (not published for this CVE) · Technical impact total (CVSS ≥ 9.0). Mission impact is CISA's Mission & Well-being decision point, and only you can judge it: high means the affected system is essential to your organisation's mission, or its compromise could cause irreversible harm to people. CISA's decision table

Published

February 10, 2021

Last Modified

November 21, 2024

Advisory Details (10)

Auto-updated Oct 4, 2026
Patch available. Sources: github_commit, redhat.
genericMentions a patch (unverified)

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/
genericMentions a patch (unverified)

[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
redhatMentions a patch (unverified)

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
redhatMentions a patch (unverified)

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

Vendor Advisories for CVE-2021-27135(1)

These vendors published their own advisory mentioning this CVE — often with vendor-specific remediation steps + affected product lists not in NVD.

Patch Availability(5)

Vendor / EcosystemFix (by version range) / 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 rangeFix by version rangeDependents
xterm—
  • every version up to 366-1: fixed in 366-1
—
Debian:12(1)
PackageVulnerable rangeFix by version rangeDependents
xterm—
  • every version up to 366-1: fixed in 366-1
—
Debian:13(1)
PackageVulnerable rangeFix by version rangeDependents
xterm—
  • every version up to 366-1: fixed in 366-1
—
Debian:14(1)
PackageVulnerable rangeFix by version rangeDependents
xterm—
  • every version up to 366-1: fixed in 366-1
—
Debian:9(1)
PackageVulnerable rangeFix by version rangeDependents
xterm327-2
  • every version up to 327-2+deb9u1: fixed in 327-2+deb9u1
—

Additional Vendor Advisories

(5)

Vendors that published advisories for this CVE beyond the curated set above. Broader coverage but minimal per-row detail — click through for the original advisory.

Data Freshness Timeline

(refreshed 9× in last 7d / 31× 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 181 total refreshes for this CVE.

  1. 2026-10-06 15:14 UTCEPSS rescore
  2. 2026-10-05 17:40 UTCEPSS rescore
  3. 2026-10-04 23:19 UTCEPSS rescore
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  8. 2026-09-30 15:33 UTCEG score recompute
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  11. 2026-09-28 13:47 UTCEPSS rescore
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  13. 2026-09-26 15:54 UTCEPSS rescore
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  15. 2026-09-26 11:25 UTCOSV refresh
  16. 2026-09-26 00:21 UTCEPSS rescore
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  1. 2026-09-15 03:06 UTCEPSS rescore
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  3. 2026-09-11 14:49 UTCEPSS rescore
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  5. 2026-09-08 21:56 UTCEPSS rescore
  6. 2026-09-07 15:58 UTCEPSS rescore
  7. 2026-09-06 23:01 UTCOSV refresh
  8. 2026-09-06 13:44 UTCEPSS rescore
  9. 2026-09-05 15:25 UTCEPSS rescore
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  18. 2026-08-28 21:37 UTCEPSS rescore
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  23. 2026-08-23 00:16 UTCEPSS rescore
  24. 2026-08-21 23:46 UTCEPSS rescore
  25. 2026-08-20 22:52 UTCEPSS rescore
  26. 2026-08-20 09:01 UTCOSV refresh
  27. 2026-08-19 17:01 UTCEPSS rescore
  28. 2026-08-18 13:45 UTCEPSS rescore
  29. 2026-08-17 13:44 UTCEPSS rescore
  30. 2026-08-16 14:53 UTCEPSS rescore
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  40. 2026-08-06 13:43 UTCEPSS rescore
  41. 2026-08-05 19:14 UTCEPSS rescore
  42. 2026-08-05 04:11 UTCOSV refresh
  43. 2026-08-04 15:06 UTCEPSS rescore
  44. 2026-08-04 10:34 UTCEPSS rescore
  45. 2026-08-03 10:33 UTCEPSS rescore
  46. 2026-08-02 02:24 UTCEPSS rescore
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  50. 2026-07-30 01:28 UTCEPSS rescore
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  52. 2026-07-28 15:33 UTCEPSS rescore
  53. 2026-07-25 14:15 UTCEPSS rescore
  54. 2026-07-24 14:15 UTCEPSS rescore
  55. 2026-07-23 14:16 UTCEPSS rescore
  56. 2026-07-23 01:59 UTCEG score recompute
  57. 2026-07-22 22:45 UTCEG score recompute
  58. 2026-07-22 14:06 UTCEPSS rescore
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  60. 2026-07-21 15:22 UTCEPSS rescore
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  62. 2026-07-20 17:05 UTCEPSS rescore
  63. 2026-07-19 14:28 UTCEPSS rescore
  64. 2026-07-19 02:27 UTCEPSS rescore
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  66. 2026-07-19 02:22 UTCOSV refresh
  67. 2026-07-18 10:02 UTCEPSS rescore
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  70. 2026-07-15 16:55 UTCEPSS rescore
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  73. 2026-07-13 22:27 UTCEPSS rescore
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  75. 2026-07-13 06:10 UTCEPSS rescore

Related CVEs(same product)

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 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 7.8% probability of exploitation in the next 30 days (94th percentile of EPSS-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?
A fix for CVE-2021-27135 is available: update to the fixed version the vendor names in its advisory. The vendor advisories EchelonGraph has for CVE-2021-27135 are linked in the Vendor Advisories panel on this page.

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