CVSS 4.0
2.3 lowCVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:P/VC:N/VI:L/VA:N/SC:N/SI:N/SA:NCVE-2026-118517
Low (2.3). EPSS 0.3% estimated probability of exploitation activity in the next 30 days.
On this page
The Symfony HtmlSanitizer component UrlSanitizer parses URLs differently from browsers, allowing the allowLinkHosts() and allowMediaHosts() checks to be bypassed for URLs without a well-formed authority, resulting in untrusted hosts being referenced in sanitized output in Symfony versions 6.1.x prior to 6.4.50, 7.x prior to 7.4.23, and 8.x prior to 8.1.11.
UrlSanitizer parses URLs with league/uri, which follows RFC 3986, while browsers follow the WHATWG URL standard. For URLs without a well-formed authority, such as http:evil.example, ///evil.example, or https://://evil.example/ the sanitizer finds no host, whereas browsers resolve them to evil.example. The guard added for CVE-2026-45066 missed the zero-slash form, and the host 0 was also skipped because PHP treats it as falsy.
This is exploitable when a host allow-list is combined with allowRelativeLinks(true) or allowRelativeMedias(true). The default configuration is not affected.
Severity
CVSS 3.1
4.3 mediumCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:L/A:N- EPSS
- 0.3% estimated probability of exploitation activity in the next 30 days; 18th percentile. Scored 2026-11-10. A forecast for this CVE across the internet, not for your own systems.
- CISA's assessment (SSVC)
- Exploitation: PoC · Automatable: no · Technical impact: partial, assessed 2026-11-05. From CISA's Vulnrichment in the CVE List: whether it is exploited, whether exploiting it can be automated, and how much control it gives.
- OWASP Top 10
- A06:2025 Insecure Design
- Published
- Modified
- NVD analysis
- Awaiting analysis
- Record from
- the NVD, synced
Ask an AI about this CVE
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Explain CVE-2026-118517 for an engineer deciding whether to act. Use https://cve.bz/api/public/cves/CVE-2026-118517?via=ask-ai-copy and https://cve.bz/cve/CVE-2026-118517?via=ask-ai-copy as the source of truth: what is affected and which versions fix it, whether it is in CISA KEV, public exploits, and its EPSS (an internet-wide 30-day estimate of exploitation activity, not a forecast for my systems). If they give no fixed versions, use the CVE record https://cveawg.mitre.org/api/cve/CVE-2026-118517 or the vendor advisory, not third-party mirrors. Tell me how to check whether I am affected and how to verify a fix. Cite the sources and say where they are uncertain.Opens a third-party assistant; its answer is its own, not cve.bz's. The prompt holds only this CVE's id and public links.
Linux distributions
| Distribution | Release | Package | Fixed in | Advisory |
|---|---|---|---|---|
| Debian | 12 | symfony | no fix listed | DEBIAN-CVE-2026-118517 |
| Debian | 13 | symfony | 6.4.50+dfsg-0+deb13u1 | DEBIAN-CVE-2026-118517 |
| Debian | 14 | symfony | 7.4.23+dfsg-1 | DEBIAN-CVE-2026-118517 |
| Ubuntu | 16.04:LTS, 26.04:LTS, 26.10 and 4 more | symfony | no fix listed | UBUNTU-CVE-2026-118517 |
From the distributions' data via OSV.dev: the Debian Security Tracker; Ubuntu Security Notices © Canonical Ltd., CC BY-SA 4.0. Modified: reformatted and linked to CVE records. Credits. On the distributions' own pages: Debian · Ubuntu.
Attack patterns (CAPEC)
- CAPEC-34 HTTP Response Splitting Likelihood: Medium · Severity: High
- CAPEC-105 HTTP Request Splitting Likelihood: Medium · Severity: High
- CAPEC-273 HTTP Response Smuggling Likelihood: Medium · Severity: High
- CAPEC-3 Using Leading 'Ghost' Character Sequences to Bypass Input Filters Likelihood: Medium · Severity: Medium
- CAPEC-6 Argument Injection Likelihood: High · Severity: High
- CAPEC-15 Command Delimiters Likelihood: High · Severity: High
- CAPEC-43 Exploiting Multiple Input Interpretation Layers Likelihood: Medium · Severity: High
- CAPEC-71 Using Unicode Encoding to Bypass Validation Logic Likelihood: Medium · Severity: High
- CAPEC-73 User-Controlled Filename Likelihood: High · Severity: High
- CAPEC-85 AJAX Footprinting Likelihood: High · Severity: Low
The attack patterns MITRE's CAPEC relates to this record's weaknesses, as MITRE names them. Credits. More on the page of CWE-184.