VulnerabilityPublished 22 Oct 2026Updated 29 Oct 2026

CVE-2026-112399: Pillow · APNG background disposal allocates full canvas before decompression bomb check

Affects aiderSource GCVE Database

Compare

Authoritative record:CVE-2026-112399· High 8.7

Not known to be exploited · CVSS 8.7 High.

Data as of 30 Oct 2026, 07:30 UTC

CVSS 4.0 base score

8.7High

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

Thin evidence

One scorer or none

CVSS scores by source
CNA (GitHub_M)	CVSS 4.0	8.7

CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N

Attack Vector: Network
Attack Complexity: Low
Attack Requirements: None
Privileges Required: None
User Interaction: None
Vulnerable system confidentiality: None
Vulnerable system integrity: None
Vulnerable system availability: High
Subsequent system confidentiality: None
Subsequent system integrity: None
Subsequent system availability: None

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

Attack Vector: Network: The vulnerable system is bound to the network stack and the set of possible attackers extends beyond the other options listed below, 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: The attacker must take no measurable action to exploit the vulnerability. The attack requires no target-specific circumvention to exploit the vulnerability. An attacker can expect repeatable success against the vulnerable system.
Attack Requirements: None: The successful attack does not depend on the deployment and execution conditions of the vulnerable system. The attacker can expect to be able to reach the vulnerability and execute the exploit under all or most instances of the vulnerability.
Privileges Required: None: The attacker is unauthorized prior to attack, and therefore does not require any access to settings or files of the vulnerable system to carry out an attack.
User Interaction: None: The vulnerable system can be exploited without interaction from any human user, other than the attacker.
Vulnerable system confidentiality: None: There is no loss of confidentiality within the Vulnerable System.
Vulnerable system integrity: None: There is no loss of integrity within the Vulnerable System.
Vulnerable system availability: High: There is a total loss of availability, resulting in the attacker being able to fully deny access to resources in the Vulnerable System; this loss is either sustained (while the attacker continues to deliver the attack) or persistent (the condition persists even after the attack has completed). Alternatively, the attacker has the ability to deny some availability, but the loss of availability presents a direct, serious consequence to the Vulnerable System (e.g., the attacker cannot disrupt existing connections, but can prevent new connections; the attacker can repeatedly exploit a vulnerability that, in each instance of a successful attack, leaks a only small amount of memory, but after repeated exploitation causes a service to become completely unavailable).
Subsequent system confidentiality: None: There is no loss of confidentiality within the Subsequent System or all confidentiality impact is constrained to the Vulnerable System.
Subsequent system integrity: None: There is no loss of integrity within the Subsequent System or all integrity impact is constrained to the Vulnerable System.
Subsequent system availability: None: There is no impact to availability within the Subsequent System or all availability impact is constrained to the Vulnerable System.

Definitions: FIRST CVSS v4.0 specification.

Exploitation evidence

Disclosed: evidence found.
CVE published 19 Oct 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

Affected software

Product	Affected	Fixed in
Homebrewaider`pkg:brew/aider`Other threats	Affected >=0.86.1_1	Fixed in–

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

Description

``` ============================================================================ APNG background disposal allocates full canvas before decompression bomb check Location: src/PIL/PngImagePlugin.py:1000 in PngImageFile._seek() Commit: a707c6b21c313880d0771e54965d142dd42358b6 ============================================================================ ``` A 126-byte animated PNG file makes Pillow's `Image.open()` allocate and fill memory sized by the image dimensions the file claims, before Pillow's built-in check for oversized images runs. A file claiming 22000×22000 pixels costs about 1.9 GB. Anyone who can get an application to open an image they supply, with default settings and no further calls such as `load()`, can cause a multi-gigabyte memory spike per file. If the claimed size exceeds the machine's free memory, the operating system kills the process outright. The bug is in `PngImageFile._seek()` in `src/PIL/PngImagePlugin.py` (around line 1000). For any APNG, `_open()` calls `self._seek(0)`. When the first `fcTL` chunk requests `OP_BACKGROUND` disposal, `_seek()` calls `Image.core.fill(self.mode, self.size)` with the full IHDR size, which allocates and zero-fills width×height×4 bytes. `OP_PREVIOUS` takes the same path, because frame 0 rewrites it to `OP_BACKGROUND`. This all happens inside the plugin factory, so `Image.open()`'s `_decompression_bomb_check(im.size)` only runs after the memory has been touched. A 1×1 frame rectangle passes the only checks on the way. Below available memory, the allocation is freed when `DecompressionBombError` propagates, so sustained pressure needs repeated or concurrent uploads. A 45000×45000 header gets the process killed by the out-of-memory killer on an 8 GB host. The attached reproducer opens two such files that differ in one byte (`dispose_op` 0 vs 1). Both end in `DecompressionBombError`, but peak resident memory is 17 MB for the first and 1864 MB for the second. The eager fill was introduced in 5e4e0fa6ee67 ("Use disposal settings from previous frame", December 2020) and first shipped in 8.1.0. Two candidate patches with a regression test are attached. ## Details For an APNG whose first `fcTL` chunk requests `OP_BACKGROUND` disposal, `PngImageFile._open()` creates and zero-fills a core image of the full IHDR-declared size. This happens inside the plugin factory, i.e. before `Image.open()` gets to `_decompression_bomb_check(im.size)`, so the check that is meant to reject oversized headers without allocating anything runs only after the allocation has been made and touched. The following 126-byte file (all chunk lengths and CRCs valid) makes `Image.open(io.BytesIO(data))`, with default `MAX_IMAGE_PIXELS` and no `load()`, reach 1.86 GB resident (`ru_maxrss`) and then raise `DecompressionBombError`. The byte-identical file with `dispose_op=0` raises the same error at 17 MB. ``` IHDR width=22000 height=22000 bit_depth=8 colour_type=6 (RGBA) acTL num_frames=2 num_plays=0 fcTL seq=0 w=1 h=1 x=0 y=0 delay=1/10 dispose_op=1 (OP_BACKGROUND) blend_op=0 IDAT zlib(00 00 00 00 00) # one 1x1 RGBA scanline IEND ``` With `width=height=45000` (8.1 GB canvas) the same call attempts the full allocation: under a 4 GiB `RLIMIT_AS` it fails with `MemoryError` from the allocator instead of `DecompressionBombError`; without a cap, on an 8 GB host with no swap, the process is OOM-killed. ### Code path `Image.open()` runs the bomb check only after the plugin's constructor (and therefore `_open()`) has returned: ```python # src/PIL/Image.py:3699-3701 im = factory(fp, filename) _decompression_bomb_check(im.size) return im ``` For a plain PNG that ordering is fine: `PngImageFile._open()` only parses chunks up to the first `IDAT` and records `self._size` from `IHDR`; nothing is allocated from it. For an APNG (`acTL` seen, so `im_n_frames` is set) `_open()` additionally positions on frame 0: ```python # src/PIL/PngImagePlugin.py:845-853 if self.png.im_n_frames is not None: … self._seek(0) ``` `_seek(0)` copies `disposal` and `bbox` from the `fcTL` chunk into `self.dispose_op` / `self.dispose_extent` and then prepares the disposal image for the *next* frame eagerly, using the full image size: ```python # src/PIL/PngImagePlugin.py:991-1001 if self._prev_im is None and self.dispose_op == Disposal.OP_PREVIOUS: self.dispose_op = Disposal.OP_BACKGROUND self.dispose = None if self.dispose_op == Disposal.OP_PREVIOUS: … elif self.dispose_op == Disposal.OP_BACKGROUND: self.dispose = Image.core.fill(self.mode, self.size) self.dispose = self._crop(self.dispose, self.dispose_extent) ``` `Image.core.fill` is `_fill()` in `src/_imaging.c:711`, which does `ImagingNewDirty(mode, xsize, ysize)` followed by `ImagingFill()`; `ImagingFill` (`src/libImaging/Fill.c:23`) writes every row, so the whole `

References

Community reviews

Loading reviews…