pypdf EUVD-2026-40425

Exploitation requires that the target application pass an attacker-supplied PDF to pypdf's parser - for example, via a web file upload endpoint, an email attachment processor, a document conversion service, or a pipeline that fetches remote PDFs. The specific triggering condition is a PDF whose content stream omits the /Length dictionary entry; this particular omission bypasses the MAX_DECLARED_STREAM_LENGTH guard. Applications that parse only internally generated or cryptographically verified PDFs are not at risk. Per the CVSS 4.0 vector (PR:N/UI:N), no authentication or user interaction is required from the attacker once a delivery path to the parser exists. Exploitation is limited to availability impact only - no confidentiality or integrity compromise is described.

The CVSS 4.0 vector AV:N/AC:L/AT:N/PR:N/UI:N reflects a low-complexity, unauthenticated, network-reachable attack - any application that accepts attacker-controlled PDFs can be targeted without special conditions. Availability impact is rated VA:L (low), suggesting partial degradation rather than guaranteed full crash, though in practice uncontrolled memory growth on constrained hosts can escalate to OOM termination. No EPSS data was provided in the input, so exploitation probability cannot be quantified. Neither a CISA KEV listing nor public PoC code was identified, placing this in a theoretical-risk category at time of analysis. The realistic priority is moderate for applications in document-processing pipelines, low-upload-trust environments, or shared infrastructure where one tenant can starve resources for others; risk is negligible for applications parsing only trusted, internally generated PDFs.

An attacker submits a crafted PDF file - containing a content stream with no /Length field - to a web application or automated document processor built on pypdf. When pypdf parses the stream, it allocates memory without bound, progressively exhausting available RAM. On shared or memory-constrained hosts this can trigger OOM kills affecting other tenants or services. No public PoC has been identified, but the attack is straightforward to construct given the detailed patch description.