Quadratic sibling re-flattening in the html_sanitize_ex traversal engine allows CPU-exhaustion denial of service
Summary
| CVE | CVE-2026-68750 |
|---|---|
| State | PUBLISHED |
| Assigner | EEF |
| Source Priority | CVE Program / NVD first with legacy fallback |
| Published | 2026-08-06 16:16:51 UTC |
| Updated | 2026-08-19 12:18:35 UTC |
| Description | Inefficient Algorithmic Complexity vulnerability in the traversal engine in rrrene html_sanitize_ex allows an unauthenticated remote attacker to exhaust server CPU and memory via a flat run of sibling elements in sanitized HTML. The list clause of HtmlSanitizeEx.Traverser.traverse/2 recurses on the tail of a sibling list and then evaluates List.flatten([head] ++ tail) over the already flattened result, so every one of n siblings copies and re-walks the entire remaining tail. The flattening is only needed for the rare case where scrub returns several replacement nodes for one node, but the cost is paid across the whole tail at every step, making traversal quadratic in sibling count. The traverser sits on every public entry point, so no particular scrubber or configuration is required and the payload needs only allowed tags. A 160 KB body of 20,000 sibling elements occupies a scheduler for roughly 1.7 seconds, and the cost grows faster than the body does. This issue affects html_sanitize_ex: from 0.3.1 before 1.4.5 and from 1.5.0-rc.0 before 1.5.3. |
Risk And Classification
Primary CVSS: v4.0 8.2 HIGH from 6b3ad84c-e1a6-4bf7-a703-f496b71e49db
CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
EPSS: 0.004410000 probability, percentile 0.368940000 (date 2026-08-19)
Problem Types: CWE-407 | CWE-407 CWE-407 Inefficient Algorithmic Complexity
| Version | Source | Type | Score | Severity | Vector |
|---|---|---|---|---|---|
| 4.0 | 6b3ad84c-e1a6-4bf7-a703-f496b71e49db | Secondary | 8.2 | HIGH | CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N/E:X/C... |
| 4.0 | CNA | CVSS | 8.2 | HIGH | CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N |
| 3.1 | [email protected] | Primary | 7.5 | HIGH | CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H |
CVSS v4.0 Breakdown
Attack Vector
NetworkAttack Complexity
LowAttack Requirements
PresentPrivileges Required
NoneUser Interaction
NoneConfidentiality
NoneIntegrity
NoneAvailability
HighSub Conf.
NoneSub Integrity
NoneSub Availability
NoneCVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
CVSS v3.1 Breakdown
Attack Vector
NetworkAttack Complexity
LowPrivileges Required
NoneUser Interaction
NoneScope
UnchangedConfidentiality
NoneIntegrity
NoneAvailability
HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
NVD Known Affected Configurations (CPE 2.3)
| Type | Vendor | Product | Version | Update | Edition | Language |
|---|---|---|---|---|---|---|
| Application | Rrrene | Htmlsanitizeex | All | All | All | All |
Vendor Declared Affected Products
| Source | Vendor | Product | Version | Platforms |
|---|---|---|---|---|
| CNA | Rrrene | Html Sanitize Ex | affected 0.3.1 1.4.5 semver | Not specified |
| CNA | Rrrene | Html Sanitize Ex | affected 1.5.0-rc.0 1.5.3 semver | Not specified |
| CNA | Rrrene | Html Sanitize Ex | affected 69ea11d61525c470b39b6860d024770d5573ff1f * git | Not specified |
References
| Reference | Source | Link | Tags |
|---|---|---|---|
| github.com/rrrene/html_sanitize_ex/commit/507a6fb95dd4c466cac8a8355d8989... | 6b3ad84c-e1a6-4bf7-a703-f496b71e49db | github.com | |
| osv.dev/vulnerability/EEF-CVE-2026-68750 | 6b3ad84c-e1a6-4bf7-a703-f496b71e49db | osv.dev | Patch, Third Party Advisory |
| github.com/rrrene/html_sanitize_ex/security/advisories/GHSA-463q-p2fr-mh9p | 6b3ad84c-e1a6-4bf7-a703-f496b71e49db | github.com | Broken Link |
| github.com/rrrene/html_sanitize_ex/commit/9f5ccedbed230930813f992a1e6906... | 6b3ad84c-e1a6-4bf7-a703-f496b71e49db | github.com | Patch |
| cna.erlef.org/cves/CVE-2026-68750.html | 6b3ad84c-e1a6-4bf7-a703-f496b71e49db | cna.erlef.org | Patch, Third Party Advisory |
| CVE Program record | CVE.ORG | www.cve.org | canonical |
| NVD vulnerability detail | NVD | nvd.nist.gov | canonical, analysis |
Vendor Comments And Credit
Discovery Credit
CNA: Peter Ullrich (en)
CNA: Jonatan Männchen / EEF (en)
CNA: René Föhring (en)
Additional Advisory Data
Workarounds
CNA: Cap the size of user-supplied HTML, and in particular the node count, before it reaches the sanitizer. The quadratic growth means the cap has to be small to be effective.
There are currently no legacy QID mappings associated with this CVE.