GHSA-4w8m-96v9-2c86 CVE-2011-4203

Moodle CRLF Injection Vulnerability in Calendar Component

Medium Packagist

Severity: Medium; The publisher's own rating, not a CVSS score
Exploit chance (EPSS): 1.18%; Chance of exploitation in the next 30 days. Higher than 67.61% of scored vulnerabilities.
Known exploited: No; Not in CISA's catalog
Weakness: CWE-113 Improper Neutralization of CRLF Sequences in HTTP Headers ('HTTP Request/Response Splitting'); CWE-93 Improper Neutralization of CRLF Sequences ('CRLF Injection')
Fix: 1.9.15; Upgrade moodle/moodle to this version or later

Description

CRLF injection vulnerability in calendar/set.php in the Calendar component in Moodle 1.9.x before 1.9.15, 2.0.x before 2.0.6, 2.1.x before 2.1.3, and 2.2 allows remote attackers to inject arbitrary HTTP headers and conduct HTTP response splitting attacks via vectors involving the url variable.

Affected versions

Packagist

Package	Vulnerable	Fixed in
moodle/moodle	`< 1.9.15`	`1.9.15`
moodle/moodle	`>= 2.0, < 2.0.6`	`2.0.6`
moodle/moodle	`>= 2.1, < 2.1.3`	`2.1.3`

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.

moodle/moodle Packagist → `1.9.15`

composer

composer require moodle/moodle:^1.9.15

Weakness

CWE-113: Improper Neutralization of CRLF Sequences in HTTP Headers ('HTTP Request/Response Splitting')

The product receives data from an HTTP agent/component (e.g., web server, proxy, browser, etc.), but it does not neutralize or incorrectly neutralizes CR and LF characters before the data is included in outgoing HTTP headers.

How to prevent it

Implementation: Construct HTTP headers very carefully, avoiding the use of non-validated input data.
Implementation: Assume all input is malicious. Use an "accept known good" input validation strategy, i.e., use a list of acceptable inputs that strictly conform to specifications. If an input does not strictly conform to specifications, reject it or transform it into something that conforms. When performing input validation, consider all potentially relevant properties, including length, type of input, the full range of acceptable values, missing or extra inputs, syntax, consistency across related fields, and conformance to business rules. As an example of business rule logic, "boat" may be syntactically valid because it only contains alphanumeric characters, but it is not valid if the input is only expected to contain colors such as "red" or "blue." Do not rely exclusively on looking for malicious or malformed inputs. This is likely to miss at least one undesirable input, especially if the code's environment changes. This can give attackers enough room to bypass the intended validation. However, denylists can be useful for detecting potential attacks or determining which inputs are so malformed that they should be rejected outright.
Implementation: Use and specify an output encoding that can be handled by the downstream component that is reading the output. Common encodings include ISO-8859-1, UTF-7, and UTF-8. When an encoding is not specified, a downstream component may choose a different encoding, either by assuming a default encoding or automatically inferring which encoding is being used, which can be erroneous. When the encodings are inconsistent, the downstream component might treat some character or byte sequences as special, even if they are not special in the original encoding. Attackers might then be able to exploit this discrepancy and conduct injection attacks; they even might be able to bypass protection mechanisms that assume the original encoding is also being used by the downstream component.
Implementation: Inputs should be decoded and canonicalized to the application's current internal representation before being validated (CWE-180). Make sure that the application does not decode the same input twice (CWE-174). Such errors could be used to bypass allowlist validation schemes by introducing dangerous inputs after they have been checked.

CWE-93: Improper Neutralization of CRLF Sequences ('CRLF Injection')

The product uses CRLF (carriage return line feeds) as a special element, e.g. to separate lines or records, but it does not neutralize or incorrectly neutralizes CRLF sequences from inputs.

How to prevent it

Implementation: Avoid using CRLF as a special sequence.
Implementation: Appropriately filter or quote CRLF sequences in user-controlled input.

References

Advisories

nvd.nist.gov/vuln/detail/CVE-2011-4203

Packages

github.com/moodle/moodle

Timeline

May 13, 2022 Published
Jan 17, 2024 Last updated by the source
Nov 1, 2026 Latest EPSS score

Advisory	Severity	Why it's related
GHSA-cg8j-5cr2-568q Moodle TeX formula editor is vulnerable to DoS through lack of execution time limits	Medium	Also affects moodle/moodle
GHSA-ggxq-2mg9-8966 Moodle has a Remote Code Execution risk via file restore	High	Also affects moodle/moodle
GHSA-8jrv-wx83-w3xj Moodle Inserts Sensitive Information Into Sent Data	Medium	Also affects moodle/moodle
GHSA-hcm6-q6pc-xfhm Moodle has an authorization logic flaw	Critical	Also affects moodle/moodle
GHSA-vwhw-vp9v-q9c9 Moodle vulnerable to Cross-site Scripting	Medium	Also affects moodle/moodle
GHSA-5cx4-w4fh-fr57 Moodle Affected by Improper Restriction of Excessive Authentication Attempts	High	Also affects moodle/moodle
GHSA-qv78-6gpp-hm68 Moodle Open Redirect vulnerability	Medium	Also affects moodle/moodle
GHSA-qfh6-h7j6-fvjv Moodle formula injection vulnerability	High	Also affects moodle/moodle

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