Path Traversal in Mako (CVE-2026-102991)
Summary
Path traversal in Mako (CVE-2026-102991). Confidential information can be exposed externally. Exploitable via TemplateLookup. Mitigation: upgrade to 1.4.2 or later.
Original description
The description as published by the source.
Summary
On Windows, a TemplateLookup URI beginning with a drive designator (e.g. C:/../../secret.txt or C:\..\..\secret.txt) bypasses the directory traversal check in Template.__init__, allowing reads of files outside the configured template directory.
This is a third, independent instance of the root cause behind CVE-2026-41205 (the // prefix) and CVE-2026-44307 (the backslash form). Both of those fixes normalized a separator spelling. Neither addressed the other way posixpath and ntpath disagree: the drive designator. Both prior fixes remain effective on their own terms; this variant survives them for an independent reason.
Details
The root cause is the same posixpath / os.path mismatch: resolution is done with posixpath, confinement is checked with os.path, which is ntpath on Windows.
# mako/lookup.py -- resolution
247: srcfile = posixpath.normpath(posixpath.join(dir_, u)) # posixpath, always
248: if os.path.isfile(srcfile): # ntpath on Windows
# mako/template.py -- confinement
268: u_norm = os.path.normpath(u_norm) # ntpath on Windows
269: if u_norm.startswith(".."): # never true for a drive URI
posixpath has no concept of a drive, so it treats C: as an ordinary path component; the .. segments pop C: and then escape the template root. ntpath, by contrast, splits the drive off and treats the remainder as rooted, discarding the .. en…
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-2026-102991 has been found in Mako.
Attackers can target a specific entry point like TemplateLookup over the network to misuse the product.
Confidential information can be exposed externally. CVSS score: 6.5/10.
What to do: upgrade Mako to 1.4.2 or later.
If unsure, ask your IT team or search "Mako CVE-2026-102991" on the vendor's site.
CVE-2026-102991 (Mako) — CWE-22 / CVSS v3 6.5
Attack vector: remote (network-reachable) / unauthenticated / no user interaction
Attack surface: TemplateLookup / Template.__init__ / posixpath / ntpath
Patched: 1.4.2 — 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.
Path traversal (CWE-22) exists in Mako. Attackers reach the vulnerable code path via TemplateLookup without authentication.
Check the vendor advisory for the affected versions of Mako. Attack surface: TemplateLookup / Template.__init__ / posixpath / ntpath.
Severity: Medium (CVSS 6.5/10). Confidential information can be exposed externally.
Update to 1.4.2.
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 'Mako' . 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 'Mako' . | 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
Mako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 Mako to 1.4.2ステージング環境で 1.4.2 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。
-
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。
Affected packages
References
- web github.com
- web github.com
- web github.com
- web github.com
- web nvd.nist.gov
- web github.com