VulnerabilityPublished 26 May 2026

CVE-2026-44214: rexxars eventsource-encoder · CRLF Injection

Affects rexxars eventsource-encoderSource CVE Database V5

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Not known to be exploited · CVSS 5.8 Medium : upgrade to 1.0.2 when convenient.

Data as of 30 Oct 2026, 11:52 UTC

CVSS 3.1 base score

5.8Medium

How severe the flaw is on the 0–10 CVSS scale.

EPSS: 0.2% chance of exploitation in 30 days – higher than 20% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
Patch: Available – fixed in 1.0.2

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

Attack Vector: Network
Attack Complexity: Low
Privileges Required: None
User Interaction: None
Scope: Changed
Confidentiality: None
Integrity: Low
Availability: None

Bold values are the worst case: easiest to exploit or largest impact.

Attack Vector: Network: The vulnerable component is bound to the network stack and the set of possible attackers extends beyond the other options listed, up to and including the entire Internet. Such a vulnerability is often termed 'remotely exploitable' and can be thought of as an attack being exploitable at the protocol level one or more network hops away (e.g., across one or more routers).
Attack Complexity: Low: Specialized access conditions or extenuating circumstances do not exist. An attacker can expect repeatable success against the vulnerable component.
Privileges Required: None: The attacker is unauthorized prior to attack, and therefore does not require any access to settings or files to carry out an attack.
User Interaction: None: The vulnerable system can be exploited without any interaction from any user.
Scope: Changed: An exploited vulnerability can affect resources beyond the security scope managed by the security authority of the vulnerable component. In this case, the vulnerable component and the impacted component are different and managed by different security authorities.
Confidentiality: None: There is no loss of confidentiality within the impacted component.
Integrity: Low: Modification of data is possible, but the attacker does not have control over the consequence of a modification, or the amount of modification is limited. The data modification does not have a direct, serious impact on the impacted component.
Availability: None: There is no impact to availability within the impacted component.

Definitions: FIRST CVSS v3.1 specification.

Exploitation evidence

Disclosed: evidence found.
CVE published 26 May 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponized: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 30 Oct 2026.

Disclosed: The CVE record is public on cve.org. Its publication is t = 0.
Detectable: A public nuclei template can find exposed instances, for defenders and attackers alike.
Weaponized: A Metasploit exploit module or Exploit-DB entry exists (Metasploit scanner modules do not count), or CISA SSVC or the CVSS exploit maturity reports a public proof of concept.
Exploited in the wild: CISA KEV lists it, CISA SSVC rates exploitation active, or a source reports attacks.
Observed by OffSeq Mirage: OffSeq Mirage honeypot sensors recorded attack traffic for this CVE, or found exposed hosts without attack traffic.

Moments are spaced evenly, not to scale; a dashed line marks a gap of six months or more. Deltas count from t = 0. Sources that give only a date (CISA KEV, Exploit-DB, or a time of exactly 00:00Z) read “same day” rather than hours. Metasploit modules carry the flaw’s disclosure date, not their release date, and nuclei templates carry no date, so both appear above but not on the timeline.

What to do

Upgrade eventsource-encoder and rexxars/eventsource-encoder to 1.0.2.

Affected software

Product	Affected	Fixed in
rexxarseventsource-encoder	Affected <1.0.2	Fixed in 1.0.2
GitHubrexxars/eventsource-encoder`pkg:github/rexxars/eventsource-encoder`Other threats	Affected <1.0.2	Fixed in 1.0.2

Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.

AI-suggested

This vulnerability is fixed in eventsource-encoder version 1.0.2. Users should upgrade to version 1.0.2 or later to remediate this issue. Patch status is not explicitly confirmed in the provided data, so users should verify the availability of the fix and any additional guidance in the vendor advisory or official project repository before deployment.

Description

CVE-2026-44214 is a medium severity vulnerability in the rexxars eventsource-encoder library versions prior to 1.0.2. The issue arises because the library does not sanitize the event or id fields of an EventSourceMessage before serialization, allowing an attacker controlling these fields to inject arbitrary CRLF sequences. This can lead to forged additional Server-Sent Events fields or entire messages on the SSE stream. The vulnerability has a CVSS score of 5.8 and is fixed in version 1.0.2. No known exploits are reported in the wild.

Impact

An attacker able to control the event or id fields can inject arbitrary CRLF sequences into SSE messages, potentially forging additional fields or messages. This impacts the integrity of the SSE stream but does not affect confidentiality or availability. The CVSS score of 5.8 reflects a medium severity with network attack vector, low attack complexity, no privileges required, no user interaction, scope changed, no confidentiality impact, limited integrity impact, and no availability impact.

Summary

The eventsource-encoder library encodes events as Server-Sent Events (SSE) messages. Versions before 1.0.2 fail to neutralize CRLF sequences in the event or id fields of EventSourceMessage objects. This improper neutralization (CWE-93) allows an attacker who controls these fields to inject line terminators (\n, \r, or \r\n), enabling them to forge additional SSE fields or entire messages within the stream. This can potentially manipulate the SSE stream's integrity. The vulnerability is addressed in version 1.0.2.

CWE-93Improper Neutralization of CRLF Sequences (CRLF Injection) (opens in a new tab)
Base weaknessOWASP Top 10 A05:2025: Injection (opens in a new tab)
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.
Implementation
Avoid using CRLF as a special sequence.
Implementation
Appropriately filter or quote CRLF sequences in user-controlled input.
OWASP Cheat Sheets
Abuse Case (opens in a new tab)
Deserialization (opens in a new tab)
Injection Prevention (opens in a new tab)
SQL Injection Prevention (opens in a new tab)
Injection Prevention in Java (opens in a new tab)
OWASP ASVS 4.0.3
V1.5.1 (opens in a new tab)
Attack patterns
Command Delimiters (opens in a new tab)
Web Server Logs Tampering (opens in a new tab)
From MITRE CWE, MITRE CAPEC and OWASP (Top 10, OpenCRE).
CWE-113Improper Neutralization of CRLF Sequences in HTTP Headers (HTTP Request Splitting) (opens in a new tab)
Variant weaknessOWASP Top 10 A05:2025: Injection (opens in a new tab)
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.
Implementation · Input Validation
Construct HTTP headers very carefully, avoiding the use of non-validated input data.
Implementation · Input Validation
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.
Implementation · Output Encoding
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.
OWASP Cheat Sheets
XML Security (opens in a new tab)
Mass Assignment (opens in a new tab)
Injection Prevention (opens in a new tab)
SQL Injection Prevention (opens in a new tab)
Injection Prevention in Java (opens in a new tab)
OWASP ASVS 4.0.3
V13.3.1 (opens in a new tab)
V5.1.4 (opens in a new tab)
V5.1.3 (opens in a new tab)
Attack patterns
HTTP Request Splitting (opens in a new tab)
Accessing/Intercepting/Modifying HTTP Cookies (opens in a new tab)
HTTP Response Splitting (opens in a new tab)
AJAX Footprinting (opens in a new tab)
From MITRE CWE, MITRE CAPEC and OWASP (Top 10, OpenCRE).

References

github.com/rexxars/eventsource-encoder/security/advisories/GHSA-m9g3-3g99-mhpx (opens in a new tab)

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Exploitation evidence

What to do

Affected software

Description

AI analysisMachine-generated, updated 2 Jun 2026, 21:20 UTC

WeaknessesCWE-93, CWE-113

Technical details

References

Community reviews

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