CVE-2026-48979 is a high-severity security vulnerability in php-standard-library/h2 (composer), affecting versions >= 6.1.0, < 6.1.2. It is fixed in 6.1.2, 6.2.1.
Impact Psl\H2\ServerConnection does not validate that the total bytes received in DATA frames match the content-length header declared in the HEADERS frame, in violation of RFC 9113 §8.1.1. A malicious client can: Send more DATA bytes than declared, smuggling additional content past application-level size limits. Send fewer DATA bytes than declared and close the stream early, causing applications that trust the declared length to behave incorrectly. The vulnerability is only reachable for consumers using Psl\H2\ServerConnection directly to accept untrusted client traffic. The high-level Psl\HTTP\Server is in active development and was not yet released at the time of this advisory; consumers of documented high-level PSL APIs are not affected. Patches Fixed in 6.1.2 and 6.2.1. Parses and validates the content-length header on incoming HEADERS (server-side only, clients do not enforce this per RFC 9110 §9.3.2). Tracks cumulative DATA frame payload length per stream. Throws StreamException on mismatch or overflow. Regression tests landed in #781, 9 of the new tests fail against the pre-fix code, proving the validation boundary is enforced. Workarounds None at the protocol layer. Applications using Psl\H2\ServerConnection directly should upgrade. Resources RFC 9113 §8.1.1 (HTTP/2 request/response exchange) RFC 9110 §8.6 (content-length header) https://github.com/php-standard-library/php-standard-library/releases/tag/6.1.2 https://github.com/php-standard-library/php-standard-library/releases/tag/6.2.1
CVE-2026-48979 has a CVSS score of 7.5 (High). The vector is network-reachable, no privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment.
A fixed version is available (6.1.2, 6.2.1). Upgrading removes the vulnerable code path.
composer
php-standard-library/h2 (>= 6.1.0, < 6.1.2)php-standard-library/h2 (>= 6.2.0, < 6.2.1)php-standard-library/php-standard-library (>= 6.1.0, < 6.1.2)php-standard-library/php-standard-library (>= 6.2.0, < 6.2.1)php-standard-library/h2 → 6.1.2 (composer)php-standard-library/h2 → 6.2.1 (composer)php-standard-library/php-standard-library → 6.1.2 (composer)php-standard-library/php-standard-library → 6.2.1 (composer)Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter instead of chasing every advisory.
Kodem's runtime-powered SCA identifies whether CVE-2026-48979 is reachable in your applications. Explore open-source security for your team.
See if CVE-2026-48979 is reachable in your applications. Get a demo
Already deployed Kodem? See CVE-2026-48979 in your environment →Upgrade the following packages to resolve this vulnerability:
php-standard-library/h2 to 6.1.2 or laterphp-standard-library/h2 to 6.2.1 or laterphp-standard-library/php-standard-library to 6.1.2 or laterphp-standard-library/php-standard-library to 6.2.1 or laterKodem Kai can prioritize this vulnerability in your dependency tree and generate a fix recommendation.
CVE-2026-48979 is a high-severity security vulnerability in php-standard-library/h2 (composer), affecting versions >= 6.1.0, < 6.1.2. It is fixed in 6.1.2, 6.2.1.
CVE-2026-48979 has a CVSS score of 7.5 (High). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
php-standard-library/h2 (composer) (versions >= 6.1.0, < 6.1.2)php-standard-library/php-standard-library (composer) (versions >= 6.1.0, < 6.1.2)Yes. CVE-2026-48979 is fixed in 6.1.2, 6.2.1. Upgrade to this version or later.
Whether CVE-2026-48979 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
php-standard-library/h2 to 6.1.2 or laterphp-standard-library/h2 to 6.2.1 or laterphp-standard-library/php-standard-library to 6.1.2 or laterphp-standard-library/php-standard-library to 6.2.1 or later