GHSA-4vpc-5jx4-cfqg CVE-2019-18886

User enumeration leak using switch user functionality in Symfony

Medium Packagist

Severity: 5.3 / 10; Medium · CVSS 3.1
Exploit chance (EPSS): 1.55%; Chance of exploitation in the next 30 days. Higher than 75.12% of scored vulnerabilities.
Known exploited: No; Not in CISA's catalog
Weakness: CWE-200 Exposure of Sensitive Information to an Unauthorized Actor; CWE-203 Observable Discrepancy
Fix: Available; 2 packages have a fixed version

Description

An issue was discovered in Symfony 4.2.0 to 4.2.11 and 4.3.0 to 4.3.7. The ability to enumerate users was possible due to different handling depending on whether the user existed when making unauthorized attempts to use the switch users functionality. This is related to symfony/security.

Affected versions

Packagist

Package	Vulnerable	Fixed in
symfony/security-http	`>= 4.1.0, < 4.2.12`	`4.2.12`
symfony/security-http	`>= 4.3.0, < 4.3.8`	`4.3.8`
symfony/symfony	`>= 4.1.0, < 4.2.12`	`4.2.12`
symfony/symfony	`>= 4.3.0, < 4.3.8`	`4.3.8`

How to fix

Move to the fixed version or later with your package manager, update the lockfile, and run your tests. If the package only arrives through another dependency, upgrade that dependency first. If none of its releases pulls a fixed version yet, force the version with your package manager's override.

symfony/security-http Packagist → `4.2.12`

composer

composer require symfony/security-http:^4.2.12

symfony/symfony Packagist → `4.2.12`

composer

composer require symfony/symfony:^4.2.12

Severity breakdown

CVSS 3.1 5.3

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N

Attack vector: Network
Attack complexity: Low
Privileges required: None
User interaction: None
Scope: Unchanged
Confidentiality: Low
Integrity: None
Availability: None

Weakness

CWE-200: Exposure of Sensitive Information to an Unauthorized Actor

The product exposes sensitive information to an actor that is not explicitly authorized to have access to that information.

How to prevent it

Architecture and Design: Compartmentalize the system to have "safe" areas where trust boundaries can be unambiguously drawn. Do not allow sensitive data to go outside of the trust boundary and always be careful when interfacing with a compartment outside of the safe area. Ensure that appropriate compartmentalization is built into the system design, and the compartmentalization allows for and reinforces privilege separation functionality. Architects and designers should rely on the principle of least privilege to decide the appropriate time to use privileges and the time to drop privileges.

CWE-203: Observable Discrepancy

The product behaves differently or sends different responses under different circumstances in a way that is observable to an unauthorized actor.

How to prevent it

Architecture and Design: Compartmentalize the system to have "safe" areas where trust boundaries can be unambiguously drawn. Do not allow sensitive data to go outside of the trust boundary and always be careful when interfacing with a compartment outside of the safe area. Ensure that appropriate compartmentalization is built into the system design, and the compartmentalization allows for and reinforces privilege separation functionality. Architects and designers should rely on the principle of least privilege to decide the appropriate time to use privileges and the time to drop privileges.
Implementation: Ensure that error messages only contain minimal details that are useful to the intended audience and no one else. The messages need to strike the balance between being too cryptic (which can confuse users) or being too detailed (which may reveal more than intended). The messages should not reveal the methods that were used to determine the error. Attackers can use detailed information to refine or optimize their original attack, thereby increasing their chances of success. If errors must be captured in some detail, record them in log messages, but consider what could occur if the log messages can be viewed by attackers. Highly sensitive information such as passwords should never be saved to log files. Avoid inconsistent messaging that might accidentally tip off an attacker about internal state, such as whether a user account exists or not.

References

Advisories

nvd.nist.gov/vuln/detail/CVE-2019-18886

Timeline

Dec 2, 2019 Published
Nov 8, 2023 Last updated by the source
Nov 1, 2026 Latest EPSS score

Advisory	Severity	Why it's related
GHSA-2v3c-qxhr-7vpv Symfony: Unbounded Recursion in the YAML Inline Lexer Lets a Single Document Crash the Process	High	Also affects symfony/symfony
GHSA-r925-mgvr-h9cc Symfony: ReDoS in HeaderUtils::split() Reachable Through the Cache-Control Request Header	High	Also affects symfony/symfony
GHSA-h5x3-xfc9-m39h Symfony: UrlGenerator Dot-Segment Encoding Skips Every Other Chained `../` or `./` → Generated URL Collapses Off-Route Under RFC 3986 Normalization	Medium	Also affects symfony/symfony
GHSA-v3wm-qf9p-c549 Symfony: HtmlSanitizer URL Parser Deny Gates Underinclusive: Percent-Encoded BiDi Marks and Unicode Whitespace Bypass Visual-Spoofing Defense	Medium	Also affects symfony/symfony
GHSA-rrj9-5q2j-4gvr Symfony: Mailomat Mailer Webhook Parser Reads the HMAC Algorithm from the Request: Signature Algorithm Downgrade	Medium	Also affects symfony/symfony
GHSA-38cx-cq6f-5755 Symfony: IpUtils::PRIVATE_SUBNETS Omits IPv6 Transition Forms (6to4, NAT64, Teredo, IPv4-compatible): SSRF Bypass in NoPrivateNetworkHttpClient	High	Also affects symfony/symfony
GHSA-6h46-9jf5-q59x Symfony: Security Firewall Bypass via failure_forward Subrequest: Unauthenticated Access to access_control-Protected GET Routes	High	Also affects symfony/security-http
GHSA-x5qj-865h-mgvm Symfony: HtmlSanitizer UrlAttributeSanitizer Misses URL Attributes	Medium	Also affects symfony/symfony

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