Vulnerability in libsixel (CVE-2026-44637)
Summary
Vulnerability in libsixel (CVE-2026-44637). Data can be tampered with by attackers. 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, a signed integer overflow in the SIXEL parser's image-buffer doubling loop can lead to an out-of-bounds heap write in sixel_decode_raw_impl. context->pos_x grows by repeat_count on every sixel character with no upper bound check. Once pos_x approaches INT_MAX, the expression "pos_x + repeat_count" used to size the image buffer overflows signed int. Depending on how the overflow wraps, the resize check that should reject oversized buffers can be bypassed, after which a subsequent write computes a large attacker-influenced offset into image->data and writes past the allocation. Reachable from any caller that decodes attacker-supplied SIXEL data, including img2sixel. 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-2026-44637 has been found in libsixel.
Data can be tampered with by attackers. CVSS score: 7.1/10.
What to do: upgrade libsixel to 1.8.7-r2 or later.
If unsure, ask your IT team or search "libsixel CVE-2026-44637" on the vendor's site.
CVE-2026-44637 (libsixel) — CWE-190 / CVSS v3 7.1
Attack vector: local / unauthenticated
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-190) exists in libsixel.
Check the vendor advisory for the affected versions of libsixel.
Severity: High (CVSS 7.1/10). Data can be tampered with by attackers.
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-2026-44637 libsixel
- Ubuntu UBUNTU-CVE-2026-44637 libsixel
References
- advisory github.com
- advisory github.com
- advisory nvd.nist.gov