Vulnerability in firefox-esr (DEBIAN-CVE-2026-6786)

Summary

Vulnerability in firefox-esr (DEBIAN-CVE-2026-6786). Successful exploitation can lead to full system takeover. Mitigation: upgrade to 140.10.0esr-1~deb11u1 or later.

Original description

The description as published by the source.

Memory safety bugs present in Firefox ESR 140.9, Thunderbird ESR 140.9, Firefox 149 and Thunderbird 149. Some of these bugs showed evidence of memory corruption and we presume that with enough effort some of these could have been exploited to run arbitrary code. This vulnerability was fixed in Firefox 150, Firefox ESR 140.10, Thunderbird 150, and Thunderbird 140.10.

Source: OSV.dev (Open Source Vulnerabilities) OSV

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 DEBIAN-CVE-2026-6786 has been found in firefox-esr.
Successful exploitation can lead to full system takeover.
What to do: upgrade firefox-esr to 140.10.0esr-1~deb11u1 or later.
If unsure, ask your IT team or search "firefox-esr DEBIAN-CVE-2026-6786" on the vendor's site.

DEBIAN-CVE-2026-6786 (firefox-esr)
Attack vector: remote (network-reachable) / unauthenticated
Patched: 140.10.0esr-1~deb11u1 — 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.

❓ What is the problem

A vulnerability (unclassified) exists in firefox-esr.

📍 Affected scope

Check the vendor advisory for the affected versions of firefox-esr.

🔥 Severity

Severity: ?. Successful exploitation can lead to full system takeover.

🔧 How to fix

Update to 140.10.0esr-1~deb11u1.

🛡️ Workaround

Until the patch is applied: disable the affected feature, apply WAF rules, or restrict access via network ACLs.

🔍 Detection

Search webserver/proxy logs for unusual request patterns matching this CVE's known IOCs. Run grep -r 'firefox-esr' . 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

1
Identify exposure identify
```
grep -r 'firefox-esr' . | 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 firefox-esr を grep し、稼働しているサービス・バージョンを把握する。
2
Apply patch patch
```
Upgrade firefox-esr to 140.10.0esr-1~deb11u1
```
ステージング環境で 140.10.0esr-1~deb11u1 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。
3
Post-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。

Affected packages

Debian:11 firefox-esr

[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"140.10.0esr-1~deb11u1"}]}]

Debian:12 firefox-esr

[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"140.10.0esr-1~deb12u1"}]}]

Debian:13 firefox-esr

[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"140.10.0esr-1~deb13u1"}]}]

Debian:14 firefox-esr

[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"140.10.0esr-1"}]}]

Debian:11 thunderbird

[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"1:140.10.0esr-1~deb11u1"}]}]

Debian:12 thunderbird

[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"1:140.10.0esr-1~deb12u1"}]}]

Debian:13 thunderbird

[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"1:140.10.0esr-1~deb13u1"}]}]

Debian:14 thunderbird

[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"1:140.10.0esr-1"}]}]

References

advisory security-tracker.debian.org