VulnerabilityPublished 26 Jun 2026

CVE-2026-48979: PHP Standard Library · HTTP/2 server-side missing content-length validation enables request smuggling

Affects php-standard-library/h2Source GCVE Database

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Not known to be exploited · CVSS 7.5 High : upgrade to 6.1.2 soon.

Data as of 30 Oct 2026, 06:59 UTC

CVSS 3.1 base score

7.5High

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

EPSS: 0.2% chance of exploitation in 30 days – higher than 18% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
Patch: Available – fixed in 6.1.2, 6.2.1

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

Attack Vector: Network
Attack Complexity: Low
Privileges Required: None
User Interaction: None
Scope: Unchanged
Confidentiality: None
Integrity: High
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: Unchanged: An exploited vulnerability can only affect resources managed by the same security authority. In this case, the vulnerable component and the impacted component are either the same, or both are managed by the same security authority.
Confidentiality: None: There is no loss of confidentiality within the impacted component.
Integrity: High: There is a total loss of integrity, or a complete loss of protection. For example, the attacker is able to modify any/all files protected by the impacted component. Alternatively, only some files can be modified, but malicious modification would present a direct, serious consequence to 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 Jun 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 29 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 php-standard-library/h2 and php-standard-library/php-standard-library to 6.1.2; php-standard-library/h2 and php-standard-library/php-standard-library to 6.2.1.

Affected software

Product	Affected	Fixed in
Packagistphp-standard-library/h2	Affected >=6.1.0 <6.1.2	Fixed in 6.1.2
Packagistphp-standard-library/h2	Affected >=6.2.0 <6.2.1	Fixed in 6.2.1
Packagistphp-standard-library/php-standard-library	Affected >=6.1.0 <6.1.2	Fixed in 6.1.2
Packagistphp-standard-library/php-standard-library	Affected >=6.2.0 <6.2.1	Fixed in 6.2.1

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

AI-suggested

A fix is available in PHP Standard Library versions 6.1.2 and 6.2.1. These versions implement proper parsing and validation of the content-length header on incoming HEADERS frames, track cumulative DATA frame payload length per stream, and throw exceptions on mismatches or overflow. Applications using Psl\H2\ServerConnection directly to accept untrusted client traffic should upgrade to these fixed versions. No protocol-layer workarounds exist.

Description

The PHP Standard Library's HTTP/2 server implementation (Psl\H2\ServerConnection) lacks validation that the total bytes received in DATA frames match the content-length header declared in the HEADERS frame, violating RFC 9113 §8.1.1. This allows a malicious client to send more or fewer DATA bytes than declared, potentially leading to request smuggling or incorrect application behavior. The vulnerability affects only consumers directly using Psl\H2\ServerConnection to accept untrusted client traffic; higher-level PSL HTTP server APIs are not affected. Fixes are available in versions 6.1.2 and 6.2.1. No protocol-layer workarounds exist, so upgrading is necessary for affected users.

Impact

A malicious client can exploit this vulnerability to smuggle additional content past application-level size limits by sending more DATA bytes than declared, or cause applications to behave incorrectly by sending fewer DATA bytes and closing the stream early. This can lead to request smuggling attacks or logic errors in applications relying on the declared content-length header. The vulnerability does not impact users of the high-level PSL HTTP server APIs. There is no indication of known exploits in the wild.

Summary

The vulnerability in PHP Standard Library's HTTP/2 server-side component (Psl\H2\ServerConnection) arises from missing validation that the cumulative DATA frame payload length matches the content-length header declared in the HEADERS frame, contrary to RFC 9113 §8.1.1. This flaw enables a malicious client to send more DATA bytes than declared, bypassing application-level size limits, or fewer bytes and close the stream early, causing misbehavior in applications trusting the declared length. The issue is limited to direct use of Psl\H2\ServerConnection for untrusted traffic; the higher-level Psl\HTTP\Server was not released at the time and is unaffected. The vulnerability is fixed in versions 6.1.2 and 6.2.1 by adding parsing and validation of content-length headers, tracking DATA frame payload length per stream, and throwing exceptions on mismatches. No protocol-layer workarounds exist, so upgrading is required.

CWE-444Inconsistent Interpretation of HTTP Requests (HTTP Request Smuggling) (opens in a new tab)
Base weaknessOWASP Top 10 A06:2025: Insecure Design (opens in a new tab)
The product acts as an intermediary HTTP agent (such as a proxy or firewall) in the data flow between two entities such as a client and server, but it does not interpret malformed HTTP requests or responses in ways that are consistent with how the messages will be processed by those entities that are at the ultimate destination.
Implementation
Use a web server that employs a strict HTTP parsing procedure, such as Apache.
Implementation
Use only SSL communication.
Implementation
Terminate the client session after each request.
OWASP Cheat Sheets
REST Assessment (opens in a new tab)
REST Security (opens in a new tab)
Cross-Site Request Forgery Prevention (opens in a new tab)
Secure Design Principles (opens in a new tab)
OWASP ASVS 4.0.3
V13.2.5 (opens in a new tab)
Attack patterns
HTTP Response Smuggling (opens in a new tab)
HTTP Request Smuggling (opens in a new tab)
From MITRE CWE, MITRE CAPEC and OWASP (Top 10, OpenCRE).

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Exploitation evidence

What to do

Affected software

Description

AI analysisMachine-generated, updated 26 Jun 2026, 22:06 UTC

WeaknessesCWE-444

Technical details

References

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