Description
X509Authenticator implements client-certificate (mTLS) authentication: the web server validates the client's certificate against a trusted CA, then passes the certificate's Subject DN (Distinguished Name: a string like CN=Alice,O=Example,emailAddress=alice@example.com) to Symfony via $SERVER['SSLCLIENTSDN']. Symfony extracts the user identifier from that string.
The extraction uses an unanchored regex that matches emailAddress= anywhere in the DN string: including inside the value of a different RDN (Relative Distinguished Name: one key=value component of the DN), such as CN. An attacker who can obtain a certificate from a trusted CA with a free-text CN can smuggle emailAddress=victim@target inside the CN value and be authenticated as the victim.
Resolution
The X509Authenticator now uses a regex that anchors the match to an RDN boundary (start of string, or following a , / / separator).
The patch for this issue is available here for branch 5.4.
Credits
Symfony would like to thank Claude Mythos Preview (via Project Glasswing) for reporting the issue and providing the fix.
Description
Symfony Mailer selects a transport via the MAILERDSN environment variable / configuration (e.g. smtp://..., sendmail://..., native://default). SendmailTransport invokes the local sendmail binary and supports two modes: -bs (speak SMTP over stdin: the default) and -t (read the message on stdin, pass recipients as command-line arguments).
In -t mode, recipient addresses are appended to the sendmail command line without a -- end-of-options separator. A recipient address beginning with - (which Symfony\Component\Mime\Address accepts as valid) is therefore interpreted by sendmail as a command-line option rather than an address.
Resolution
The SendmailTransport transport now ensure -- is set before the list of recipients.
The patch for this issue is available here for branch 5.4.
Credits
Symfony would like to thank Claude Mythos Preview (via Project Glasswing) for reporting the issue and providing the fix.
Description
Symfony\Component\Yaml\Parser resolves YAML aliases (anchor) during parsing. Aliases that reference collections (arrays, stdClass, TaggedValue-wrapped collections) can themselves point to other collections containing aliases, creating exponential expansion at resolution time. A small input can blow up into a multi-gigabyte structure and exhaust memory: the classic "Billion Laughs" denial-of-service against any parser exposed to untrusted YAML.
Resolution
The Parser now counts collection alias resolutions in a shared ParserState object, with a default limit of 128, following the SnakeYAML model. Scalar aliases remain unrestricted since they cannot drive exponential growth. The limit is configurable via a new $maxAliasesForCollections argument on Parser::construct(), Yaml::parse() and Yaml::parseFile(). A new Yaml::PARSEEXCEPTIONONALIAS flag also rejects all aliases outright when parsing fully untrusted input.
The patch for this issue is available here for branch 5.4.
Credits
Symfony would like to thank Pietro Tirenna (Shielder) for reporting the issue and Nicolas Grekas for fixing it.
Description
Symfony\Component\Yaml\Parser::cleanup() strips the optional %YAML directive header, leading comments, and document start/end markers before parsing. The original regexes contained overlapping quantifiers, most notably '#^%YAML[: ][\d.]+.\n#u', whose [\d.]+ and . overlap on the dot, that exhibit catastrophic backtracking on crafted input. A single oversized %YAML directive header (or comment / document-marker line) makes the parser hang for an arbitrarily long time, denying service.
Resolution
The four regexes in Parser::cleanup() (YAML directive header, leading comments, document-start marker, document-end marker) have been rewritten with possessive quantifiers and unambiguous character classes so backtracking cannot occur.
The patch for this issue is available here for branch 5.4.
Credits
Symfony would like to thank Pietro Tirenna (Shielder) for reporting the issue and Nicolas Grekas for fixing it.
Description
symfony/dom-crawler provides the Crawler class for navigating HTML/XML documents with CSS/XPath selectors; symfony/browser-kit's HttpBrowser uses it to parse fetched pages.
Crawler::addXmlContent() sets DOMDocument::$validateOnParse = true before calling loadXML(). Setting validateOnParse re-enables libxml's DTD subset processing, including external entity resolution, even though LIBXMLNONET is passed. LIBXMLNONET blocks network fetches but not file:// entities. An attacker-supplied XML document with a SYSTEM "file:///etc/passwd" entity is therefore expanded.
Resolution
The Crawler::addXmlContent method does not set the validateOnParse flag anymore.
The patch for this issue is available here for branch 5.4.
Credits
Symfony would like to thank Claude Mythos Preview (via Project Glasswing) for reporting the issue and providing the fix.
Description
When a firewall is configured with form-login (or any authenticator using DefaultAuthenticationFailureHandler) and the failureforward: true option, the handler reads the failurepath parameter from the failing login request and uses it as the path of an internal subrequest dispatched through HttpKernelInterface::SUBREQUEST.
Symfony's Firewall::onKernelRequest listener intentionally skips subrequests under the assumption they are internally generated and trusted, which also means AccessListener (the listener that evaluates accesscontrol) does not run. Because the attacker controls the target of the subrequest, an unauthenticated POST to the check path with failurepath=/admin/whatever performs a local request forgery that executes the target controller outside the firewall perimeter and returns its response to the caller.
Applications that follow Symfony's recommended best practice of protecting administrative areas with broad accesscontrol rules (e.g. ^/admin requires ROLEADMIN) and expose read-only GET endpoints under that area (data exports, internal APIs, account views) are fully exposed: any such GET route can be read by an unauthenticated attacker without any developer misconfiguration, debug mode, or state-changing GET handler being required.
Resolution
DefaultAuthenticationFailureHandler no longer honors the request-supplied failurepath parameter when failureforward is enabled. The subrequest is always dispatched to the configured failurepath option (defaulting to loginpath), which is set by the application owner and not by the request. The redirect branch (failureforward: false) is unchanged because redirects re-enter the firewall on the next request and are not subject to this bypass.
The patch for this issue is available here for branch 5.4.
Credits
Symfony would like to thank Nguyen Ngoc Toan Thang (@a-tt-om) and Tran Quoc Tri Trung (@teebow1e) for reporting the issue, and Nicolas Grekas for providing the fix.
Description
Symfony\Bridge\Monolog\Command\ServerLogCommand (the server:log console command) is a development-time helper that opens a TCP listener and displays log records pushed to it by the application's logging pipeline. Two unsafe defaults combine into a remotely reachable PHP object-deserialization sink:
1. The listener binds to 0.0.0.0:9911 by default; it accepts connections on every interface, not only loopback. 2. Each received frame is processed as unserialize(base64decode($message)) without an allowedclasses allowlist, without authentication, and without any integrity check. The decoded value is then passed to displayLog(..., array $record) which assumes (without validating) that the result is an array.
Any host that can reach TCP port 9911 on a machine running server:log can therefore submit attacker-chosen serialized PHP payloads. The minimum impact is an unauthenticated denial of service (sending a non-array, e.g. serialize(new stdClass()), crashes the listener with a type error). Object injection with magic-method side effects (wakeup() / destruct() / etc.) is reachable before the array type-check fires; full remote code execution is environment-dependent and contingent on usable gadget chains in the autoload set of the target process.
Resolution
The server:log command no longer binds to all interfaces by default: the default --host is now 127.0.0.1:9911, requiring explicit opt-in to accept off-host traffic. Message decoding is gated by an unserialize() allowlist restricted to the Symfony\Component\VarDumper\Caster\ and Symfony\Component\VarDumper\Cloner\ classes that legitimately appear inside dumped log records; any other class is rejected and the record discarded.
The patch for this issue is available here for branch 5.4.
Credits
Symfony would like to thank Toàn Thắng and Sam Sanoop for reporting the issue and Nicolas Grekas for fixing it.
Description
Symfony\Component\Yaml\Parser is the entry point for parsing YAML strings into PHP values via Yaml::parse(). When the parser is exposed to attacker-controlled input, deeply nested mappings or sequences cause both the block-level (Parser::parseBlock()) and inline (Inline::parseSequence() / Inline::parseMapping()) parsers to recurse without a depth limit. A crafted document exhausts the PHP stack and crashes the worker.
Resolution
The Parser now tracks recursion depth in a shared ParserState object across both block-level and inline parsing, with a default limit of 128. The limit is configurable via a new $maxNestingLevel argument on Parser::construct(), Yaml::parse() and Yaml::parseFile().
The patch for this issue is available here for branch 5.4.
Credits
Symfony would like to thank Pietro Tirenna (Shielder) for reporting the issue and Nicolas Grekas for fixing it.
Description
The Request class improperly interprets some PATHINFO in a way that leads to representing some URLs with a path that doesn't start with a /. This can allow bypassing some access control rules that are built with this /-prefix assumption.
Resolution
The Request class now ensures that URL paths always start with a /.
The patch for this issue is available here for branch 5.4.
Credits
We would like to thank Andrew Atkinson for discovering the issue, Chris Smith for reporting it and Nicolas Grekas for providing the fix.
Description
Symfony\Component\Cache\Adapter\PdoAdapter is the PDO-backed cache adapter. Its clear($prefix) method (inherited from AbstractAdapterTrait) is documented to delete cache items whose key starts with $prefix.
In the non-versioning code path, the caller-supplied $prefix is concatenated into $namespace = $this->namespace.$prefix and passed to PdoAdapter::doClear(), which builds:
sql DELETE FROM <table> WHERE <idcol> LIKE '<namespace>%'
The value is interpolated directly into the SQL text and executed with PDO::exec(): $namespace is not bound. A caller able to influence $prefix can break out of the literal and inject SQL, expanding deletion scope from the intended prefix to arbitrary rows, or otherwise reshape query semantics.
Most applications don't expose clear($prefix) to untrusted input directly, but the contract of the method is to safely accept any prefix string, so the lack of escaping is a defect of the adapter itself.
Resolution
AbstractAdapterTrait::clear() now rejects any $prefix containing characters outside [-+.A-Za-z0-9]: when an invalid prefix is supplied, the method logs a warning and returns false instead of reaching the SQL layer. This blocks quotes, %, null bytes and other characters that would let an attacker break out of the LIKE literal.
The patch for this issue is available here for branch 5.4.
Credits Symfony would like to thank secsyscodex for reporting the issue and Nicolas Grekas for fixing it.
Description
Symfony\Component\Mime\Header\ParameterizedHeader (and the related parameter handling reachable from Symfony\Component\Mime\Header\Headers) is responsible for serializing structured headers such as Content-Type and Content-Disposition, which carry key=value parameters (e.g. Content-Disposition: attachment; filename="x").
RFC 2045 / RFC 5322 require parameter names to be tokens: a restricted ASCII subset that excludes whitespace, CR/LF, and the tspecials set. Symfony's parameter handling validates and properly encodes parameter values, but does not validate parameter names: the supplied name is emitted verbatim into the serialized header.
A caller that derives a parameter name from untrusted input, e.g. an application that lets a user influence a Content-Disposition parameter name, can include \r\n or other non-token bytes inside the name, terminating the current header and injecting additional headers in the rendered message. This is the classic CRLF / header-injection primitive applied to the parameter-name slot.
Resolution
ParameterizedHeader now rejects parameter names that contain bytes outside the RFC token character class.
The patch for this issue is available here for branch 5.4.
Credits
Symfony would like to thank Fabian Fleischer for reporting the issue and Alexandre Daubois for fixing it.
Description
Some Twig filters in CodeExtension use "issafe=html" but don't actually ensure their input is safe.
Resolution
Symfony now escapes the output of the affected filters.
The patch for this issue is available here for branch 4.4.
Credits
We would like to thank Pierre Rudloff for reporting the issue and to Nicolas Grekas for providing the fix.
Description
Symfony\Component\Routing\Generator\UrlGenerator::doGenerate() percent-encodes . and .. path segments so that the generated URL still resolves to the originating route after RFC 3986 §5.2.4 dot-segment removal (which strict RFC-3986 consumers — routers, reverse proxies, HTTP clients — perform before percent-decoding).
The encoding was implemented as strtr($url, ['/../' => '/%2E%2E/', '/./' => '/%2E/']) plus a trailing-segment fixup. strtr advances past the trailing / of each match, so the next dot-segment in a chained sequence was left unescaped:
| Input | Output (before fix) | Expected | | -------------------- | ---------------------------------------- | ----------------------------------- | | /../../../ | /%2E%2E/../%2E%2E/ | /%2E%2E/%2E%2E/%2E%2E/ | | /foo/../../../bar | /foo/%2E%2E/../%2E%2E/bar | /foo/%2E%2E/%2E%2E/%2E%2E/bar |
When a route exposes a parameter constrained by a permissive requirement (.+, ., or similar) that accepts dots and slashes, attacker-controlled chained .. or . segments produce a generated URL that, under strict RFC 3986 normalization, collapses to a different path than the originating route. The Twig path() / url() helpers and any server-side use of UrlGenerator are affected. Same class of route round-trip integrity issue as CVE-2026-45065.
Note: WHATWG-conformant browsers treat %2E/%2E%2E as dot-segments during URL parsing, so the encoding never protected browser-side traversal. The defense exists for RFC-3986-conformant consumers; restoring it for chained segments closes the gap there.
Resolution
UrlGenerator now matches every /. or /.. dot-segment in a single left-to-right pregreplacecallback pass using a lookahead that does not consume the trailing /, so adjacent dot-segments are encoded correctly.
The patches for this issue are available here for branch 5.4 (and forward-ported to 6.4, 7.4, 8.0 and 8.1).
Credits
Symfony would like to thank Alex Pott for reporting the issue and Nicolas Grekas for providing the fix.
Description
Symfony routes can declare a requirements regex per path parameter, e.g. a route /{locale}/blog with requirements: { locale: 'en|fr|de' }. The Twig path() / url() helpers (backed by UrlGenerator) validate supplied parameter values against that regex before building the URL.
UrlGenerator constructs the validation pattern as '#^'.$req.'$#', where $req is the raw requirement string. For a requirement expressed as an alternation, e.g. locale: 'ar|bg|...|vi|...|zhCN' (very common), ^ and $ anchor only the first and last alternatives, so any middle alternative matches as an unanchored substring. A value like /evil.com satisfies the requirement (because it contains vi), and the generated path becomes //evil.com/...: a protocol-relative URL the browser navigates off-site.
Resolution
The UrlGenerator class now wraps the requirement in a non-capturing group so the ^ and $ anchors apply to the whole alternation.
The patch for this issue is available here for branch 5.4.
Credits
Symfony would like to thank Claude Mythos Preview (via Project Glasswing) for reporting the issue and providing the fix.