symfony: Authentication Bypass by Spoofing
CVE-2026-118513 is a high-severity authentication bypass by spoofing vulnerability in symfony from Sensiolabs, with a CVSS 4.0 base score of 7.7 out of 10. It can be exploited remotely over the network by an attacker with a low-privileged account, without any action from a user. The record lists versions 5.4.56, 6.4.50, 7.4.23 as the first without the flaw, so updating symfony to one of those releases or later removes the exposure. There is no confirmed exploitation so far. EPSS estimates a 0.27% chance of exploitation within 30 days, which is low compared with other CVEs.
High severity with no evidence of exploitation so far.
What to do
- Update symfony to 5.4.56 or 6.4.50 or 7.4.23 or 8.1.11, whichever matches your release line, or a later version.
- Read the advisory on github.com for workarounds and exact fixed builds.
Affected products and versions
| Vendor | Product | Affected versions | Fixed in |
|---|---|---|---|
| Sensiolabs | symfony | before 5.4.56; 6.0.0 up to, but not including, 6.4.50; 7.0.0 up to, but not including, 7.4.23; 8.0.0 up to, but not including, 8.1.11 | 5.4.56, 6.4.50, 7.4.23, 8.1.11 |
Version data comes from the organisation that assigned the CVE. Confirm against the vendor advisory before deciding you are unaffected.
How the severity score breaks down
- Attack vector
- NetworkCan be exploited remotely over a network, including the internet.
- Attack complexity
- LowNo special conditions are needed; the attack works reliably.
- Attack requirements
- PresentThe target must be in a specific state or configuration for the attack to work.
- Privileges required
- LowA basic user account is enough.
- User interaction
- NoneNo action by a victim is required.
- Confidentiality (vulnerable system)
- HighSerious loss of confidentiality on the vulnerable system.
- Integrity (vulnerable system)
- HighSerious loss of integrity on the vulnerable system.
- Availability (vulnerable system)
- HighSerious loss of availability on the vulnerable system.
- Confidentiality (other systems)
- NoneNo loss of confidentiality on systems beyond the vulnerable one.
- Integrity (other systems)
- NoneNo loss of integrity on systems beyond the vulnerable one.
- Availability (other systems)
- NoneNo loss of availability on systems beyond the vulnerable one.
Vector: CVSS:4.0/AV:N/AC:L/AT:P/PR:L/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/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. Scored by CNA.
Official description
Authentication bypass by spoofing in X509Authenticator and X509AuthenticationListener of 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 allows an attacker holding a certificate from the application's trusted CA who can influence the CN to authenticate as an arbitrary user of the application, including a privileged one, following an incomplete fix for CVE-2026-45063. X509Authenticator extracts the user identifier from the Subject DN (Distinguished Name) that the web server passes in $_SERVER['SSL_CLIENT_S_DN']. The fix for CVE-2026-45063 anchored that extraction to an RDN (Relative Distinguished Name) boundary, but the regular expression used was not escape-aware. The expression runs against an already serialized DN, so it cannot tell an RDN separator from a separator character that occurs inside a value. Under RFC 2253, used by Apache and by nginx's $ssl_client_s_dn, a comma inside a value is escaped as \, and the expression reads it as a separator regardless. RFC 2253 also does not treat / as a separator, so it leaves it bare inside a value, while the expression treats every / as one. The legacy X509_NAME_oneline() format, used by Apache's LegacyDNStringFormat and by nginx's $ssl_client_s_dn_legacy, is the mirror image: it escapes / as \/ and leaves , bare. In that format, a certificate with no emailAddress attribute, or whose poisoned CN precedes it, authenticates as the smuggled address. To cover both RFC 2253 and the legacy X509_NAME_oneline() format, X509Authenticator and X509AuthenticationListener now split the DN into RDNs before looking for the attribute, instead of matching the attribute against the serialized string. They select the separator from the serialization, split on unescaped occurrences of that separator only, unescape each RDN afterwards with the rules of its format, and require the attribute to span a whole RDN. The accepted value grammar is unchanged. Applications that pass a per-attribute user key (such as SSL_CLIENT_S_DN_Email) and deployments whose CA generates or validates the subject are not affected by this vulnerability.
Source: the CVE record as published by its numbering authority, via NVD and CVE.org.
The underlying weakness: Authentication Bypass by Spoofing
This attack-focused weakness is caused by incorrectly implemented authentication schemes that are subject to spoofing attacks.
More Authentication Bypass by Spoofing vulnerabilities (CWE-290)
Timeline
- CVE record published.
- CISA published its SSVC assessment (exploitation: none, automatable: no, technical impact: total).
- Record last changed materially (score, affected products, status or references).
References
Patches and release notes
Other vulnerabilities in symfony
- 8.4 High severity
- 8.7 High severity
- 8.2 High severity
- 8.2 High severity
- 8.7 High severity
- 8.7 High severity
Recent Authentication Bypass by Spoofing vulnerabilities
- 9.8 Critical severity
- 8.1 High severity
- 9.3 Critical severity
- 7.9 High severity
- 7.1 High severity
- 9.1 Critical severity
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