vulnerability / NVI-00007068 / Revision 4
Symfony has an HtmlSanitizer allowLinkHosts() / allowMediaHosts() Bypass via URL-Parser Differentials and Misclassification
OSV carries this publisher advisory for symfony/html-sanitizer, symfony/html-sanitizer, symfony/html-sanitizer, symfony/symfony, symfony/symfony. This is an aggregated source copy; consult the original publisher and compare update dates.
This report has not inspected your inventory, configuration, deployed build, reachability or evidence. A catalog listing and a severity score do not establish exposure or compromise.
01 / Meaning
Why it matters
Published affected context helps an owner decide what evidence to gather. This report has not examined your application.
6.1 MEDIUM (3.1)
nvd@nist.gov severity; no combined Null risk score.
2.3 LOW (4.0)
security-advisories@github.com severity; no combined Null risk score.
0.338%
FIRST EPSS model v2026.06.15; exploitation probability over 30 days, percentile 0.27226. Missing scores are unknown.
As of · FIRST EPSS
02 / Applicability
The affected context
Affected versions, configuration prerequisites and known exclusions are public. Confirm each one against the deployed service.
symfony/html-sanitizer
source listedECOSYSTEM: introduced 6.1.0; fixed 6.4.40
### Description `symfony/html-sanitizer` lets applications sanitise untrusted HTML. The configuration methods `allowLinkHosts([...])` and `allowLinkSchemes([...])` are intended to restrict `` targets to an allowlist of hosts/schemes; `allowMediaHosts()` / `allowMediaSchemes()` do the same for `` etc. Three distinct bypasses allow a content author to smuggle off-allowlist URLs past these checks. First, `UrlSanitizer::parse()` parses the input following RFC-3986, while browsers follow the WHATWG URL Standard which normalises `\` to `/` before parsing the authority of "special" schemes; so an input like `https://evil\@trusted.com/` parses with host `trusted.com` server-side but navigates to `https://evil/` in the browser. Second, WHATWG collapses any run of `/` after the scheme into `//`, while RFC-3986 does not; so `https:/evil.com/` and `https:///evil.com/` parse as host-less (skipping the host allowlist) but resolve to `evil.com` in the browser. Third, `UrlAttributeSanitizer` checks `'a' === $element` to route to the link policy and falls through to the media policy otherwise, but `` is a navigable hyperlink equivalent to ``; so `` was sanitis
symfony/html-sanitizer
source listedECOSYSTEM: introduced 7.0.0; fixed 7.4.12
### Description `symfony/html-sanitizer` lets applications sanitise untrusted HTML. The configuration methods `allowLinkHosts([...])` and `allowLinkSchemes([...])` are intended to restrict `` targets to an allowlist of hosts/schemes; `allowMediaHosts()` / `allowMediaSchemes()` do the same for `` etc. Three distinct bypasses allow a content author to smuggle off-allowlist URLs past these checks. First, `UrlSanitizer::parse()` parses the input following RFC-3986, while browsers follow the WHATWG URL Standard which normalises `\` to `/` before parsing the authority of "special" schemes; so an input like `https://evil\@trusted.com/` parses with host `trusted.com` server-side but navigates to `https://evil/` in the browser. Second, WHATWG collapses any run of `/` after the scheme into `//`, while RFC-3986 does not; so `https:/evil.com/` and `https:///evil.com/` parse as host-less (skipping the host allowlist) but resolve to `evil.com` in the browser. Third, `UrlAttributeSanitizer` checks `'a' === $element` to route to the link policy and falls through to the media policy otherwise, but `` is a navigable hyperlink equivalent to ``; so `` was sanitis
symfony/html-sanitizer
source listedECOSYSTEM: introduced 8.0.0; fixed 8.0.12
### Description `symfony/html-sanitizer` lets applications sanitise untrusted HTML. The configuration methods `allowLinkHosts([...])` and `allowLinkSchemes([...])` are intended to restrict `` targets to an allowlist of hosts/schemes; `allowMediaHosts()` / `allowMediaSchemes()` do the same for `` etc. Three distinct bypasses allow a content author to smuggle off-allowlist URLs past these checks. First, `UrlSanitizer::parse()` parses the input following RFC-3986, while browsers follow the WHATWG URL Standard which normalises `\` to `/` before parsing the authority of "special" schemes; so an input like `https://evil\@trusted.com/` parses with host `trusted.com` server-side but navigates to `https://evil/` in the browser. Second, WHATWG collapses any run of `/` after the scheme into `//`, while RFC-3986 does not; so `https:/evil.com/` and `https:///evil.com/` parse as host-less (skipping the host allowlist) but resolve to `evil.com` in the browser. Third, `UrlAttributeSanitizer` checks `'a' === $element` to route to the link policy and falls through to the media policy otherwise, but `` is a navigable hyperlink equivalent to ``; so `` was sanitis
symfony/symfony
source listedECOSYSTEM: introduced 6.1.0; fixed 6.4.40
### Description `symfony/html-sanitizer` lets applications sanitise untrusted HTML. The configuration methods `allowLinkHosts([...])` and `allowLinkSchemes([...])` are intended to restrict `` targets to an allowlist of hosts/schemes; `allowMediaHosts()` / `allowMediaSchemes()` do the same for `` etc. Three distinct bypasses allow a content author to smuggle off-allowlist URLs past these checks. First, `UrlSanitizer::parse()` parses the input following RFC-3986, while browsers follow the WHATWG URL Standard which normalises `\` to `/` before parsing the authority of "special" schemes; so an input like `https://evil\@trusted.com/` parses with host `trusted.com` server-side but navigates to `https://evil/` in the browser. Second, WHATWG collapses any run of `/` after the scheme into `//`, while RFC-3986 does not; so `https:/evil.com/` and `https:///evil.com/` parse as host-less (skipping the host allowlist) but resolve to `evil.com` in the browser. Third, `UrlAttributeSanitizer` checks `'a' === $element` to route to the link policy and falls through to the media policy otherwise, but `` is a navigable hyperlink equivalent to ``; so `` was sanitis
symfony/symfony
source listedECOSYSTEM: introduced 7.0.0; fixed 7.4.12
### Description `symfony/html-sanitizer` lets applications sanitise untrusted HTML. The configuration methods `allowLinkHosts([...])` and `allowLinkSchemes([...])` are intended to restrict `` targets to an allowlist of hosts/schemes; `allowMediaHosts()` / `allowMediaSchemes()` do the same for `` etc. Three distinct bypasses allow a content author to smuggle off-allowlist URLs past these checks. First, `UrlSanitizer::parse()` parses the input following RFC-3986, while browsers follow the WHATWG URL Standard which normalises `\` to `/` before parsing the authority of "special" schemes; so an input like `https://evil\@trusted.com/` parses with host `trusted.com` server-side but navigates to `https://evil/` in the browser. Second, WHATWG collapses any run of `/` after the scheme into `//`, while RFC-3986 does not; so `https:/evil.com/` and `https:///evil.com/` parse as host-less (skipping the host allowlist) but resolve to `evil.com` in the browser. Third, `UrlAttributeSanitizer` checks `'a' === $element` to route to the link policy and falls through to the media policy otherwise, but `` is a navigable hyperlink equivalent to ``; so `` was sanitis
symfony/symfony
source listedECOSYSTEM: introduced 8.0.0; fixed 8.0.12
### Description `symfony/html-sanitizer` lets applications sanitise untrusted HTML. The configuration methods `allowLinkHosts([...])` and `allowLinkSchemes([...])` are intended to restrict `` targets to an allowlist of hosts/schemes; `allowMediaHosts()` / `allowMediaSchemes()` do the same for `` etc. Three distinct bypasses allow a content author to smuggle off-allowlist URLs past these checks. First, `UrlSanitizer::parse()` parses the input following RFC-3986, while browsers follow the WHATWG URL Standard which normalises `\` to `/` before parsing the authority of "special" schemes; so an input like `https://evil\@trusted.com/` parses with host `trusted.com` server-side but navigates to `https://evil/` in the browser. Second, WHATWG collapses any run of `/` after the scheme into `//`, while RFC-3986 does not; so `https:/evil.com/` and `https:///evil.com/` parse as host-less (skipping the host allowlist) but resolve to `evil.com` in the browser. Third, `UrlAttributeSanitizer` checks `'a' === $element` to route to the link policy and falls through to the media policy otherwise, but `` is a navigable hyperlink equivalent to ``; so `` was sanitis
03 / Response
What to do next
- vendor patch
The original advisory lists fixed boundaries 6.4.40 for symfony/html-sanitizer. Confirm the publisher’s latest guidance.
Confirm current vendor support, compatibility and deployment evidence. This report has not tested a fix in your system. GitHub Advisory Database via OSV
- vendor patch
The original advisory lists fixed boundaries 7.4.12 for symfony/html-sanitizer. Confirm the publisher’s latest guidance.
Confirm current vendor support, compatibility and deployment evidence. This report has not tested a fix in your system. GitHub Advisory Database via OSV
- vendor patch
The original advisory lists fixed boundaries 8.0.12 for symfony/html-sanitizer. Confirm the publisher’s latest guidance.
Confirm current vendor support, compatibility and deployment evidence. This report has not tested a fix in your system. GitHub Advisory Database via OSV
- vendor patch
The original advisory lists fixed boundaries 6.4.40 for symfony/symfony. Confirm the publisher’s latest guidance.
Confirm current vendor support, compatibility and deployment evidence. This report has not tested a fix in your system. GitHub Advisory Database via OSV
- vendor patch
The original advisory lists fixed boundaries 7.4.12 for symfony/symfony. Confirm the publisher’s latest guidance.
Confirm current vendor support, compatibility and deployment evidence. This report has not tested a fix in your system. GitHub Advisory Database via OSV
- vendor patch
The original advisory lists fixed boundaries 8.0.12 for symfony/symfony. Confirm the publisher’s latest guidance.
Confirm current vendor support, compatibility and deployment evidence. This report has not tested a fix in your system. GitHub Advisory Database via OSV
- investigate
Identify the exact component and deployed version, examine the linked publisher’s conditions, and retain evidence of any mitigation.
Confirm current vendor support, compatibility and deployment evidence. This report has not tested a fix in your system. FIRST EPSS
A fixed release is not deployment evidence.
Check current vendor support and compatibility. After making a change, verify the deployed build and relevant runtime conditions. Keep the evidence, owner and time. An updated lockfile alone does not prove what is running.
04 / Limits
What this report cannot establish
- Customer inventory, deployment, reachability and exploitation have not been inspected.
- NVD lastModified does not establish freshness of every associated CPE record.
05 / Provenance
Sources you can inspect
Each assertion retains its source. Mirrored records may repeat one underlying publisher; additional links are not independent corroboration.
- GHSA-qc95-4862-92fh ↗
GitHub Advisory Database via OSV · vendor advisory
Observed . GitHub-origin advisory, CC-BY-4.0; OSV is an aggregate copy, not independent corroboration.
- CVE-2026-45066 ↗
NIST National Vulnerability Database · official catalog
Observed . This product uses data from the NVD API but is not endorsed or certified by the NVD.
- CVE-2026-45066 ↗
FIRST EPSS · official catalog
Observed . FIRST EPSS; probability of exploitation in the next 30 days, not local compromise. Dataset date/model retained; FIRST services terms apply.
Public revision history
Only published revisions appear here. Routine fetches do not create a material-change event.
- Revision 4 ·
Source facts changed; compare the preserved prior revision.
- Revision 2 ·
Dated EPSS estimate updated; this is not a new disclosure or proof of exploitation.
- Revision 1 ·
First indexed by Null; source disclosure date is shown separately.