Vulnerability in libsixel (CVE-2026-44636)
Summary
Vulnerability in libsixel (CVE-2026-44636). Successful exploitation can lead to full system takeover. Mitigation: upgrade to 1.8.7-r2 or later.
Original description
The description as published by the source.
libsixel is a SIXEL encoder/decoder implementation derived from kmiya's sixel. From to 1.8.7-r1, signed integer overflow in sixel_encode_highcolor's allocation size calculation can lead to a heap buffer overflow. The public sixel_encode entry point validates only that width and height are greater than zero, with no upper bound. width and height are multiplied as plain int when computing the allocation size for paletted_pixels and normalized_pixels. Any caller that asks libsixel to encode a pixel buffer with width times height greater than INT_MAX (about 2.15 billion) will hit a wrapped allocation size; under the right wrap, the malloc succeeds with a buffer much smaller than the encoder expects, and the encoder writes past the end of the heap allocation. This vulnerability is fixed in 1.8.7-r2.
Source: NIST National Vulnerability Database NVD GitHub Advisory
Auto-generated summary
Assembled by SecPulse from the source data (CVSS, CWE, affected versions) using templates — no AI involved. Check the original description and references below for exact details.
A vulnerability tracked as CVE-2026-44636 has been found in libsixel.
Successful exploitation can lead to full system takeover. CVSS score: 7.4/10.
What to do: upgrade libsixel to 1.8.7-r2 or later.
If unsure, ask your IT team or search "libsixel CVE-2026-44636" on the vendor's site.
CVE-2026-44636 (libsixel) — CWE-122 / CVSS v3 7.4
Attack vector: local / unauthenticated / no user interaction
Patched: 1.8.7-r2 — apply immediately
Plan: 1) Audit SBOM/dependencies, 2) Stage→prod upgrade, 3) Add WAF/proxy monitoring on affected endpoints, 4) Hunt IOCs in logs.
Refs: see the GHSA / vendor advisory / patched release linked on this page.
A vulnerability (CWE-122) exists in libsixel.
Check the vendor advisory for the affected versions of libsixel.
Severity: High (CVSS 7.4/10). Successful exploitation can lead to full system takeover.
Update to 1.8.7-r2.
Until the patch is applied: disable the affected feature, apply WAF rules, or restrict access via network ACLs.
Search webserver/proxy logs for unusual request patterns matching this CVE's known IOCs. Run grep -r 'libsixel' . against your dependency files (package-lock.json, requirements.txt, go.sum) to find affected services.
Response actions
Concrete steps and command examples for SOC/SRE teams to execute in order
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1Identify exposure identify
grep -r 'libsixel' . | grep -v node_modulesリポジトリと本番環境の依存ファイル (package-lock.json / requirements.txt / go.sum / Gemfile.lock 等) で
libsixelを grep し、稼働しているサービス・バージョンを把握する。 -
2Apply patch patch
Upgrade libsixel to 1.8.7-r2ステージング環境で 1.8.7-r2 に上げて回帰テスト → 本番反映。回帰テストはアプリの主要ハッピーパスを含めること。
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3Post-deployment verification verify
Confirm patched version is live in productionパッチ適用後、ステージングで PoC または同等の悪用パターンを再現して脆弱性が閉じたことを確認。本番ではアクセスログ・WAF でアラート再発が無いか継続監視。
Fix status by distribution
Fixed packages published by each distribution for this CVE
- Debian DEBIAN-CVE-2026-44636 libsixel
- Ubuntu UBUNTU-CVE-2026-44636 libsixel
References
- advisory github.com
- advisory github.com
- advisory nvd.nist.gov