VulnerabilityPublished 29 Oct 2026

CVE-2026-96639: Aider · Pillow multi-frame loaders can reuse stale native image storage after mode transitions

Affects aiderSource GCVE Database

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Authoritative record:CVE-2026-96639· Critical 9.8

Not known to be exploited · CVSS 9.8 Critical.

Data as of 30 Oct 2026, 07:30 UTC

CVSS 3.1 base score

9.8Critical

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 3.1	9.8

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

Attack Vector: Network
Attack Complexity: Low
Privileges Required: None
User Interaction: None
Scope: Unchanged
Confidentiality: High
Integrity: High
Availability: High

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: High: There is total loss of confidentiality, resulting in all resources within the impacted component being divulged to the attacker. Alternatively, access to only some restricted information is obtained, but the disclosed information presents a direct, serious impact.
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: High: There is total loss of availability, resulting in the attacker being able to fully deny access to resources in the impacted component; 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 impacted component (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).

Definitions: FIRST CVSS v3.1 specification.

Exploitation evidence

Disclosed: evidence found.
CVE published 21 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–

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Description

### Summary Pillow multi-frame image loaders can retain native `ImagingCore` storage allocated for one frame while changing the Python-side image `mode` and decoder tiles for a later frame. If frame 0 allocates storage for a narrow mode such as `L`, and a later frame of the same dimensions switches to a wider mode such as `RGB` or `CMYK`, Pillow may decode wider pixels into the stale narrow native buffer. This causes native out-of-bounds writes and process crashes. In the MPO/JPEG path, I also demonstrated command execution in matching Python/Pillow runtime profiles through Pillow's documented `ImageSequence.Iterator` + `frame.load()` path. ### Details The root cause appears to be that `ImageFile.load_prepare()` only reallocates native storage when `_im is None`. It does not verify that the retained native `ImagingCore` storage still matches `self.mode` and `self.size`. Several multi-frame `seek()` / `_open()` paths can update `self._mode` and decoder tiles for a later frame without invalidating `_im`. The decoder then writes or reads according to the new frame mode while the native storage still belongs to the old frame mode. Verified affected surfaces: 1. **PSD** `PsdImageFile.seek()` can switch from grayscale/native `L` storage to RGB layer decoding while retaining `_im`. This produces attacker-controlled native out-of-bounds writes and reliable crashes. 2. **MPO/JPEG** A crafted two-frame MPO can make frame 0 allocate `L` storage, then make frame 1 decode `CMYK` / `RGB` data into the retained `L` storage. The documented `ImageSequence.Iterator` path reaches this with `frame.load()`. Verified native memory corruption, crash, over-read behavior, and scoped harmless-marker command execution on Pillow 12.3.0. 3. **DCX** `DcxImageFile.seek()` calls `PcxImageFile._open()`, which changes mode/tile state without a native-storage mode guard. A crafted DCX with `L` then `RGB` PCX frames produces retained-storage mismatch and crash. 4. **MIC** MIC can call `TiffImageFile._open()` directly and bypass TIFF's normal guarded `seek()` behavior. With a `NextIFD`-based reachable frame transition, this produces retained-storage mismatch and crash. TIFF appears to be a useful positive control because its `seek()` path checks both size and mode before reusing storage. ### Impact - process crash / denial of service, - native out-of-bounds write, - native over-read in the MPO path. Stronger proven impact: - command execution in matching Python/Pillow runtime profiles through the MPO/JPEG path. Server-side deployment impact: - Create a local vulnerable web upload service that accepts an unauthenticated MPO upload and automatically processes it with Pillow. - The attack is one HTTP request and requires no user interaction after upload. - The fixed harmless command-output marker succeeded 10/10 times. - The `_im=None` control was clean 10/10 times. ## Reproduction Evidence Tested version: ```text Pillow 12.3.0 ``` MPO terminal proof environments: ```text Python 3.12.3 + Pillow 12.3.0, clean PyPI environment: marker 10/10, control 0/10 Python 3.13.14 + Pillow 12.3.0, prepared profile: marker 10/10, control 0/10 ``` Server-side web-upload proof: ```text control 1..10: MARKER_MISSING control_summary ok 0 missing 10 /10 vulnerable 1..10: MARKER_OK marker_output <server-user> vulnerable_summary ok 10 missing 0 /10 ``` The terminal proof uses a fixed harmless marker command only. It does not use a reverse shell, persistence, data exfiltration, or arbitrary attacker-selected commands. I can provide the following private artifacts to maintainers: - minimal crash fixtures for PSD, MPO, DCX, and MIC, - non-weaponized MPO marker PoC, - local vulnerable web upload demo, - gdb/GEF geometry receipts, - control-run logs, - proposed regression-test shape. ## Minimal Reproduction Shape For the MPO path, the vulnerable consumer shape is: ```python from io import BytesIO from PIL import Image, ImageSequence source = BytesIO(open(path, "rb").read()) image = Image.open(source) iterator = ImageSequence.Iterator(image) next(iterator).load() next(iterator).load() ``` The crafted image shape is: ```text frame 0: mode L, dimensions W x H frame 1: same W x H, wider mode such as CMYK ``` Frame 0 allocates native `L` storage. Frame 1 changes the logical mode and decoder state but can reuse the old native storage. The frame 1 decoder writes using the wider mode into the narrow storage. ## Suggested Fix Direction Before reusing native `ImagingCore` storage, Pillow should verify that the retained storage is compatible with the current logical image mode and size. A central guard in `ImageFile.load_prepare()` could compare native storage mode/size against `self.mode` / `self.size` and allocate fresh storage when they differ. Alternatively, every mode-changing `seek()` / `_open()` path should explicitly invalidate `_im` before decoding. Caution: TIFF has specialized tile-size behavior and already has a mo

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