Symfony: Ip Constraint public/private Modes Accept IPv4-Mapped and IPv4-Compatible IPv6 Addresses allowing SSRF Filter Bypass
- Exploited
- No known exploitation
- Fix
- Fixed in 5.4.56, 6.4.50, 7.4.23, 8.1.11
- Who is exposed
- Not reported
Do first: Upgrade to a fixed version: 5.4.56, 6.4.50, 7.4.23, 8.1.11.
- Last modified
- A 0-100 score for how much a CVE matters across the industry: exploitation, exposure, how widely the software is used, severity and whether a fix exists.What do these mean? →
- 36/100 · provisional
- Whether working attack code is public (Exploit-DB, Metasploit, Nuclei or GitHub). Public code makes attacks easier.What do these mean? →
- None on Exploit-DB, Metasploit or GitHub
- Exploitation: none
- Automatable: yes
- Technical impact: partial
Summary
The Symfony Validator component's Ip constraint, when used in its public or private filtered modes, can accept some internal addresses as public, including IPv4-mapped and IPv4-compatible IPv6 addresses that embed internal IPv4 addresses. An attacker can reach this remotely without logging in, and an application that relies on the constraint to block internal targets before making a server-side request can be exposed to server-side request forgery.
Written by anthropic/claude-haiku-5.5 from the sources below. Verify against them.
Read the original description
The Symfony Validator component IpValidator incompletely classifies internal addresses in the filtered modes of the Ip constraint, so some internal addresses are accepted as public, which can lead to Server-Side Request Forgery (SSRF) 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.
In these modes, IpValidator relies on the PHP flags FILTER_FLAG_NO_PRIV_RANGE and FILTER_FLAG_NO_RES_RANGE to classify addresses as public, private, or reserved. These flags do not cover shared address space (100.64.0.0/10) or IPv4-mapped, IPv4-compatible, and 6to4 IPv6 addresses, which can embed internal IPv4 addresses. A value such as ::ffff:127.0.0.1 can therefore pass validation even though it points to an internal host. Applications that rely on the Ip constraint to reject internal addresses, for example before making a server-side request to a user-supplied address, can be exposed to SSRF.
cve.now Index
- Exploitation0/40No signal
- Exposure20/25No login or user action needed per the CVSS vector, CISA rates it automatable · Unknown: No advisory context yet
- Reach10/20Affects Packagist packages
- Severity6.3/10CVSS 6.3
- No patch0/5No signal
What would change the score
- Would score about 81 if added to CISA KEV
- Would score about 76 if CISA's SSVC rates exploitation active
- Would score about 41 if advisories confirm default setups are exposed
What to do
Upgrade to a fixed version: 5.4.56, 6.4.50, 7.4.23, 8.1.11.
Timeline
- CVE published
- First seen by cve.now
- CISA SSVC assessment
Exploitation: none · Automatable: yes · Technical impact: partial
- Record last updated
Affected versions
- symfony/validatorPackagist
fixed in 5.4.56; From 6.0.0 · fixed in 6.4.50; From 7.0.0 · fixed in 7.4.23; From 8.0.0 · fixed in 8.1.11
Evidence 2
- Advisory
- Patch
Corrections
None so far.
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Questions about CVE-2026-123125
Is CVE-2026-123125 being exploited?
It is not in CISA's Known Exploited Vulnerabilities catalog, and CISA's SSVC assessment does not mark exploitation as active. That does not mean it has not been attacked: vendors and researchers can report attacks before CISA lists them. No public exploit code is tracked.Source: cve.now feed data
Which versions are affected by CVE-2026-123125?
symfony/validator (Packagist): before 5.4.56; from 6.0.0 before 6.4.50; from 7.0.0 before 7.4.23; from 8.0.0 before 8.1.11.Source: cve.now feed data
How do I fix CVE-2026-123125?
Upgrade to a fixed version: 5.4.56, 6.4.50, 7.4.23, 8.1.11.Source: cve.now feed data