CVE-2026-33021

HIGHNVD 7.37.3—
EchelonGraph scoreMEDIUM confidence

This high-severity CVE scores 7.3 under NVD CVSS v3. EPSS exploit probability: 0.2%, top 84% of all CVEs by exploit prediction. GitHub Security Advisory data not yet ingested — confidence will rise once GHSA publishes (typical lag: hours to days for open-source ecosystem CVEs; never for infrastructure-only CVEs).

Triggered by: NVD CVSS baseline
Sources: epss, nvd
Elevated
7.3EG
EchelonGraph verdictPlan a fixSerious severity, but no confirmed exploitation yet.
  • High severity, but no confirmed exploitation yet
CISA-KEV: Not listedEPSS PROB: 0%CVSS: 7.3Exploit: Elevated riskExposed: 0

No vendor fix yet — apply a workaround or compensating control (WAF / firewall / segmentation) and watch for a patch.

libsixel is a SIXEL encoder/decoder implementation derived from kmiya's sixel. Versions 1.8.7 and prior contain a use-after-free vulnerability in sixel_encoder_encode_bytes() because sixel_frame_init() stores the caller-owned pixel buffer pointer directly in frame->pixels without making a defensive copy. When a resize operation is triggered, sixel_frame_convert_to_rgb888() unconditionally frees this caller-owned buffer and replaces it with a new internal allocation, leaving the caller with a dangling pointer. Any subsequent access to the original buffer by the caller constitutes a use-after-free, confirmed by AddressSanitizer. An attacker who controls incoming frames can trigger this bug repeatedly and predictably, resulting in a reliable crash with potential for code execution. This issue has been fixed in version 1.8.7-r1.

CVSS v3
7.3
EG Score
7.3(medium)
EG Risk
49(Track)
EG Risk 49/100SSVC: 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
Severity73% × 45%
Exploitation40% × 40%
Automatability0% × 15%
Action: Routine — remediate on your standard cadence.
EPSS PROB
0%
EPSS %ILE
16%
KEV
Not listed

Published

April 14, 2026

Last Modified

July 25, 2026

Advisory Details (2)

Auto-updated Jun 14, 2026
🔬 Proof of concept available. Patch available. Sources: github_release, github.
github Patch Available🟡 PoC Available

Use-after-free in sixel_encoder_encode_bytes() · Advisory · saitoha/libsixel · GitHub

https://github.com/saitoha/libsixel/security/advisories/GHSA-j6m5-2cc7-3whc
github_release Patch Available

v1.8.7-r1 security update

Patch available: saitoha/libsixel v1.8.7-r1

https://github.com/saitoha/libsixel/releases/tag/v1.8.7-r1

Affected Packages

(4 across 4 ecosystems)
Debian:11(1)
PackageVulnerable rangeFixed inDependents
libsixel1.10.3-1 ... 1:1.8.7-r2-1 (12 versions)——
Debian:12(1)
PackageVulnerable rangeFixed inDependents
libsixel1.10.3-3 ... 1:1.8.7-r2-1 (9 versions)——
Debian:13(1)
PackageVulnerable rangeFixed inDependents
libsixel1.10.5-1 ... 1:1.8.7-r2-1 (8 versions)——
Debian:14(1)
PackageVulnerable rangeFixed inDependents
libsixel1.10.5-1 ... 1:1.8.7-6 (7 versions)1:1.8.7-r2-1—

Weakness Classification(1)

MITRE Common Weakness Enumeration — the root-cause categories this CVE belongs to.

Data Freshness Timeline

(refreshed 5× in last 7d / 29× 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 163 total refreshes for this CVE.

  1. 2026-09-13 16:47 UTCEPSS rescore
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  1. 2026-08-19 17:03 UTCEPSS rescore
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Related CVEs(same CWE)

Frequently asked(5)

What is CVE-2026-33021?
CVE-2026-33021 is a high vulnerability published on April 14, 2026. libsixel is a SIXEL encoder/decoder implementation derived from kmiya's sixel. Versions 1.8.7 and prior contain a use-after-free vulnerability in sixelencoderencodebytes() because sixelframeinit() stores the caller-owned pixel buffer pointer directly in frame->pixels without making a defensive…
When was CVE-2026-33021 disclosed?
CVE-2026-33021 was first published in the National Vulnerability Database on April 14, 2026, with the most recent update on July 25, 2026. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
Is CVE-2026-33021 actively exploited?
CVE-2026-33021 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 0% probability of exploitation in the next 30 days, which ranks it in the top 83.9% of all scored CVEs.
What is the CVSS score of CVE-2026-33021?
CVE-2026-33021 has a CVSS v3 base score of 7.3 (NVD).
How do I remediate CVE-2026-33021?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2026-33021, 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.

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