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CVE.org (no NVD analysis yet)· CNA Checkmarx

CVE-2026-121949: Symfony: HtmlSanitizer Does Not URL-Sanitize srcset and imagesrcset: Media Scheme and Host Allow-List Bypass

LowCVSS 2.3 · v4.0—No exploit Fix available

Noroxi assessment

Priority: Monitor (action score 9/100)

  • The sources we track (CISA KEV, Exploit-DB, Metasploit, Nuclei, GitHub) show no public exploit code or exploitation in the wild.
  • Probability of exploitation in the next 30 days: 0.23% (FIRST EPSS).
  • Anyone who can reach it over the internet can trigger it. No account or password is required. No special conditions are required; it is repeatable.
  • Fixed version: sensiolabs symfony 6.4.50, 7.4.23, 8.1.11.

Low priority for now. Upgrade to sensiolabs symfony 6.4.50, 7.4.23, 8.1.11 or later.

Generated automatically from the record's data: CVSS (NVD and CNA), CISA KEV and SSVC, FIRST EPSS, exploit sources, fixed versions. How we calculate it

Primary sources: NVD · CVE.org · FIRST EPSS

The Symfony HtmlSanitizer component does not apply the media URL policy to the srcset and imagesrcset attributes, allowing values that point to hosts or schemes not permitted by allowMediaSchemes() or allowMediaHosts() to bypass it, so that browsers load images from disallowed hosts 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.The srcset attribute on img and source elements and the imagesrcset attribute on link elements are allowed by the sanitizer, but their URL candidates are never validated, so their values are kept verbatim while the same URL in src is dropped. The fixes for CVE-2026-45753 and CVE-2026-48761 extended the same attribute list but did not cover these two attributes. For example, with allowMediaSchemes(['https']) and allowMediaHosts(['trusted.example']), <img srcset="https://evil.example/a.png 1x"> survives sanitization, and the browser fetches the selected candidate as it would fetch src. Candidates with a scheme forbidden by the configuration, such as http, are kept as well. Any application that sanitizes untrusted HTML and relies on the media schemes and hosts allowlists to restrict where images can be loaded from is affected. A single crafted value is enough to make the browser of a user viewing the sanitized content send a request to an attacker-controlled host, which can be used to track viewers or log their IP addresses. No authentication is needed if the application accepts HTML from unauthenticated users.

Published
Nov 5, 2026
Updated
Nov 6, 2026
EPSS
0.2% · 15th percentile

Report tools

JSON

Action score

9

Monitor

Low priority for now.

CVSS
9 / 40 · 2.3 / 10
CISA KEV
0 / 30 · Not listed
EPSS
0 / 30 · 0.2%

CISA SSVC decision

Exploitation
none
Automatable
no
Technical impact
partial

Vulnrichment: CISA's decision-tree inputs.

CNA vs NVD score

NVD
—
CNA · Checkmarx
2.3
NVD has not scored this yet; the score shown is the CNA’s.

CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:P/VC:N/VI:N/VA:N/SC:L/SI:L/SA:N

The score given by the assigning authority versus NVD’s independent score. A gap means the severity is contested.

Get told when this record changes

  • Not in KEV: no record of exploitation in the wild
  • No public exploit code on record
  • A fix has been released

If any of these changes, we'll tell you in the daily email digest.

Follow CVE-2026-121949

When you'll hear from us

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  • when exploit code appears or is weaponized
  • when the record is updated (including a fixed version)
  • when EPSS rises 20 points in a week

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Noroxi analysis

What does it mean in your environment?

The assessment above is generated automatically from the record's data; it doesn't know your environment. Our team verifies on your systems whether this vulnerability is actually exploitable and which mitigation is enough.

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Affected systems

Is your version affected?

Pick the product and type the version you run. It's compared with this record's version ranges in your browser; the version isn't sent anywhere.

—

Versions reported by the vendor

Affected version ranges reported by the assigning authority (Checkmarx). Independent of NVD's CPE analysis and usually ahead of it.

  • sensiolabs symfony

    • 6.1.0 and later · before 6.4.50affected · git
    • 7.0.0 and later · before 7.4.23affected · git
    • 8.0.0 and later · before 8.1.11affected · git

Package-level exposure

OSV and GitHub Advisory data: ecosystem, package and range. SBOM matching uses this table.

EcosystemPackageAffected rangeFix
Debian:12symfonyfrom 0—
Debian:13symfonybefore 6.4.50+dfsg-0+deb13u16.4.50+dfsg-0+deb13u1
Debian:14symfonybefore 7.4.23+dfsg-17.4.23+dfsg-1

Same product

sensiolabs: all records

Other highest-scoring records for the same primary product.

  • CVE-2019-18889An issue was discovered in Symfony 3.4.0 through 3.4.34, 4.2.0 through 4.2.11, and 4.3.0 through 4.3.7.
    49Plan
  • CVE-2018-14773An issue was discovered in Http Foundation in Symfony 2.7.0 through 2.7.48, 2.8.0 through 2.8.43, 3.3.0 through 3.3.17, 3.4.0 through…
    43Plan
  • CVE-2019-10910In Symfony before 2.7.51, 2.8.x before 2.8.50, 3.x before 3.4.26, 4.x before 4.1.12, and 4.2.x before 4.2.7, when service ids allow user…
    41Plan

Published before and after this one in the same product

  • ← EarlierCVE-2026-123125Nov 5, 2026 · Symfony: Ip Constraint public/private Modes Accept IPv4-Mapped and IPv4-Compatible IPv6 Addresses allowing SSRF Filter Bypass
    25Monitor
  • ← EarlierCVE-2026-118517Nov 5, 2026 · Symfony: HtmlSanitizer allowLinkHosts() / allowMediaHosts() Bypass via URLs Without a Well-Formed Authority (Incomplete Fix for CVE-2026-45066)
    9Monitor
  • Later →CVE-2026-123746Nov 6, 2026 · Symfony: Programmatic Logins Skip the checkPostAuth() Method of User Checkers
    9Monitor

Remediation

Which version to upgrade to

Fix versions compiled from the vendor, package registries and Microsoft. Verify the vendor's note before upgrading.

Product / packageFixed versionSource
sensiolabs symfony6.4.50Vendor (CNA)
sensiolabs symfony7.4.23Vendor (CNA)
sensiolabs symfony8.1.11Vendor (CNA)
debian:symfony6.4.50+dfsg-0+deb13u1 · Debian:13Package registry (OSV)
debian:symfony7.4.23+dfsg-1 · Debian:14Package registry (OSV)

Exploit status

No known public exploit

No public exploit has been observed yet. That doesn't mean you're safe, only that the bar is a little higher.

Research context

For pentesters and researchers: attack profile, score disagreement, timeline, patch commits, credits, variant and chain candidates, bug bounty scope. All derived from existing data; no exploit code.

Timeline

From publication to today: proof of concept, Metasploit module, CISA KEV and fix record. Dates are as reported by the sources.

  1. Published
  2. Fix recordedsame day
  3. TodayNov 13, 2026+8 d
EPSS, last 120 days

FIRST EPSS daily score; only changes of 0.01 or more are recorded (step chart).

Patch and commit links

Commit, PR and diff links among the references. A starting point for patch-diffing and variant hunting; fixes, not exploits.

Credits

All researchers

Finders, reporters and analysts named in the CNA record. Click a name for that researcher’s other records.

Variant candidates

Same product, same weakness class, within 18 months. If the patch missed the root cause, the sibling bug is here.

  • CVE-2026-48736114 days apartSymfony: IpUtils::PRIVATE_SUBNETS Omits IPv6 Transition Forms (6to4, NAT64, Teredo, IPv4-compatible): SSRF Bypass in NoPrivateNetworkHttpClient
    27Monitor
  • CVE-2026-1231250 days apartSymfony: Ip Constraint public/private Modes Accept IPv4-Mapped and IPv4-Compatible IPv6 Addresses allowing SSRF Filter Bypass
    25Monitor
  • CVE-2026-1185170 days apartSymfony: HtmlSanitizer allowLinkHosts() / allowMediaHosts() Bypass via URLs Without a Well-Formed Authority (Incomplete Fix for CVE-2026-45066)
    9Monitor
  • CVE-2026-45066114 days apartSymfony: HtmlSanitizer allowLinkHosts() / allowMediaHosts() Bypass via URL-Parser Differentials and <area> Misclassification
    9Monitor

Not on record for this CVE: public bounty program.

Technical details

Attack conditions

  • Anyone who can reach it over the internet can trigger it.
  • No account or password is required.
  • No special conditions are required; it is repeatable.

If successful

Confidentiality
Integrity
Availability
Attack vector
Network
Attack complexity
Low
Privileges required
None
User interaction
P
Scope
X

Weakness class (CWE)

CWE-184 · Incomplete List of Disallowed Inputs

CVSS vector

CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:P/VC:N/VI:N/VA:N/SC:L/SI:L/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

nvd-secondary

Attack context

MITRE CAPEC attack patterns and ATT&CK techniques for this weakness class (CWE). A starting point for detection rules and threat hunting.

ATT&CK techniques

—

Change log

  1. SSVC exploitation— → none
  2. Exploit maturity— → none
  3. Fix✗ → ✓

For records you follow, these changes also arrive as notifications. →

References

Show all references (1 more)

Vendor advisories and official records. Exploit/PoC links are deliberately left out.

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