DNS rebinding in Symfony HttpClient exposes internal hosts and ports
Key facts
- Attack vector
- Network
- Privileges required
- Low
- User interaction
- None
- Attack complexity
- Low
- Attack requirements
- Present
- Impact type
- —
- Confidentiality · integrity · availability
- None · None · None
- Fix status
- Fixed
Attack profile from CVSS 4.0 · CNA. Fix status from CNA.
Summary
Symfony before 5.4.56, 6.x before 6.4.50, 7.x before 7.4.23 and 8.x before 8.1.11 has a flaw in HttpClient's NoPrivateNetworkHttpClient (CWE-367). It passes the checked IP only on a host's first lookup, so later requests resolve the host again. An attacker who controls a host's DNS can answer with a public IP first and a private IP later, so the client connects to private addresses. Differing errors for open and closed ports let the attacker enumerate internal hosts and ports.
Written with Claude Haiku 5.5 from the sources below · 2026-11-07
Description from the CNA
The Symfony HttpClient component NoPrivateNetworkHttpClient does not pin the checked IP address of cached hosts, allowing for DNS rebinding to bypass private network restrictions, resulting in enumeration of internal hosts and ports in Symfony versions prior to 5.4.56, 6.x prior to 6.4.50, 7.x prior to 7.4.23, and 8.x prior to 8.1.11. NoPrivateNetworkHttpClient resolves the host of each request and checks the IP before connecting. It caches the result per host, and passes the IP to the decorated client through the resolve option so that the client connects to the exact IP that was checked. The issue is that resolve was only passed on the first lookup of a host: on subsequent requests, the decorated client resolved the host again on its own. An attacker who controls a host's DNS can exploit this with DNS rebinding by answering the first lookup with a public IP, and subsequent lookups with a private IP, so when an application sends several requests to that host through the same client, the later requests connect to the private IP. This happens, for example, when an application fetches several URLs of a repository provided by a user. The check of the primary_ip in the on_progress callback still aborts the request before anything is sent, but the connection is made, and the error differs depending on whether the port is open or closed. This allows enumerating internal hosts and ports, as in CVE-2024-50342.
Why it matters now
SSVC decision points
CISA ADP · SSVC 2.0.3
- Exploitation
- None
- Automatable
- No
- Technical impact
- Partial
The decision (Track, Attend, Act) also depends on your mission and well-being impact; see CISA's SSVC guide.
Affected products
No affected products listed by the sources yet.
Remediation
Upgrade Symfony to 5.4.56, 6.4.50, 7.4.23 or 8.1.11, depending on the branch in use.
Written with Claude Haiku 5.5 from the sources below · 2026-11-07
Fixed in the same release
Records fixed by the same vendor advisory or release, as the CNA lists them.
- Release ·
sensiolabs symfony 5.4.56, 6.4.50 and 2 more versions
2 records Highest priority Priority LOW 2 LOW
Other records, highest priority first
- TI-2026-85494 Symfony Ip constraint accepts internal addresses as publicPriority LOW 33
Vendor assessments
Timeline
- 2026-11-05 Threatist record created from CVE-2026-123119
- 2026-11-05 CISA SSVC decision points changed
- 2026-11-07 Affected versions changed · Red Hat
- 2026-11-07 CVSS score added · Red Hat
References
More sensiolabs vulnerabilities
- TI-2019-13616 An issue was discovered in Symfony 3.4.0 through 3.4.34, 4.2.0 through 4.2.11, and 4.3.0… CVSS 3.1CRITICAL 9.8
- TI-2018-10604 An issue was discovered in Http Foundation in Symfony 2.7.0 through 2.7.48, 2.8.0 through… CVSS 3.1MEDIUM 6.5
- TI-2019-08131 In 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… CVSS 3.1CRITICAL 9.8
- TI-2016-02159 Symfony before 2.8.6 and 3.x before 3.0.6 allows remote attackers to bypass… CVSS 3.0CRITICAL 9.8
- TI-2019-08459 An issue was discovered in Symfony before 4.2.12 and 4.3.x before 4.3.8. CVSS 3.1CRITICAL 9.8
- TI-2018-08136 An issue was discovered in the Ldap component in Symfony 2.8.x before 2.8.37, 3.3.x… CVSS 3.0CRITICAL 9.8
Sources
- CVE-2026-123119 · CVE Program
- CVE-2026-123119 · NVD
- FIRST EPSS
- CVE-2026-123119 · Red Hat security data · CC BY 4.0
This product uses the NVD API but is not endorsed or certified by the NVD. Sources and licences